Vena-caval blood pump

ABSTRACT

Apparatus and methods are described for improving renal function of a patient, including mechanically occluding the patient&#39;s inferior vena cava downstream of the renal vein ostium to form an upstream region and a downstream region of the inferior vena cava, and mechanically pumping blood through the inferior vena cava from the upstream region to a discharge location in the downstream region while the inferior vena cava is occluded, wherein the blood remains in the inferior vena cava while being mechanically pumped. Other applications are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of continuation of U.S. patentapplication Ser. No. 16/278,323 to Schwammenthal (published as US2019/0175807), filed Feb. 18, 2019, which is continuation of U.S. patentapplication Ser. No. 16/022,445 to Schwammenthal (issued as U.S. Pat.No. 10,363,350), filed Jun. 28, 2018, which is continuation of U.S.patent application Ser. No. 14/774,081 to Schwammenthal (issued as U.S.Pat. No. 10,039,874), which is the US national phase application of PCTApplication No. PCT/IL/2014/050289 to Schwammenthal (published as WO14/141284), filed Mar. 13, 2014, which claims priority from:

U.S. Provisional Patent Application 61/779,803 to Schwammenthal, filedMar. 13, 2013, entitled “Renal pump;” and

U.S. Provisional Patent Application 61/914,475 to Schwammenthal, filedDec. 11, 2013, entitled “Renal pump.”

The present application is related to International Patent ApplicationPCT/IL2013/050495 to Tuval (published as WO 13/183060), filed Jun. 6,2013, entitled “Prosthetic renal valve,” which claims priority from U.S.Provisional Patent Application 61/656,244 to Tuval, filed Jun. 6, 2012,entitled “Prosthetic renal valve.”

All of the above-listed applications are incorporated herein byreference.

FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to medicalapparatus. Specifically, some applications of the present inventionrelate to apparatus and methods associated with placing a pump in one ormore of a subject's renal veins.

BACKGROUND

It is common for cardiac dysfunction or congestive heart failure todevelop into kidney dysfunction, which in turn, causes congestive heartfailure symptoms to develop or worsen. Typically, systolic and/ordiastolic cardiac dysfunction causes systemic venous congestion, whichgives rise to an increase in renal venous and interstitial pressure. Theincrease in the pressure causes fluid retention by the body to increasedue both to kidney dysfunction and renal neurohormonal activation, bothof which typically develop as a result of the increase in renal venousand interstitial pressure. The resulting fluid retention causescongestive heart failure to develop or worsen, by causing a blood volumeoverload at the heart and/or by increasing systemic resistance.Similarly, it is common for kidney dysfunction and/or renalneurohormonal activation to develop into cardiac dysfunction and/orcongestive heart failure. This pathophysiological cycle, in whichcardiac dysfunction and/or congestive heart failure leads to kidneydysfunction and/or renal neurohormonal activation, or in which kidneydysfunction and/or renal neurohormonal activation leads to cardiacdysfunction and/or congestive heart failure, each dysfunction leading todeterioration in the other dysfunction, is called the cardio-renalsyndrome.

Increased renal venous pressure has been experimentally shown to causeazotemia, and a reduction in glomerular filtration rate, renal bloodflow, urine output, and sodium excretion. It has also been shown toincrease plasma renin and aldosterone, and protein excretion. Venouscongestion may also contribute to anemia via three different pathways: Areduction in the kidney's erythropoietin production, hemodilution byfluid retention, and an inflammatory response leading to a reducedgastro-intestinal iron uptake.

Mechanistically, increased renal venous pressure, may causeintracapsular pressure and, subsequently, interstitial peritubularpressure, to rise. A rise in peritubular pressure may impact tubularfunction (reduce sodium excretion), as well as diminish glomerularfiltration by raising the pressure in the Bowman capsule.

In heart failure patients, increased renal venous pressure may not onlyresult from increased central venous (right atrial) pressure, but alsofrom intraperitoneal fluid accumulations (ascites) exerting directpressure on the renal veins. Reduction of intraabdominal pressure inheart failure patients by removal of fluid (e.g., via paracentesis,and/or ultrafiltration) has been shown to reduce plasma creatininelevels.

Increased venous return resulting from activation of the “leg musclepump” during physical activity such as walking may raise systemic venouspressure, particularly in heart failure patients, and may result inreflux into the renal veins.

SUMMARY OF EMBODIMENTS

In accordance with some applications of the present invention, a bloodpump that includes an impeller is placed inside a subject's renal veinand the impeller is activated to pump blood from the renal vein to thesubject's vena cava, in order to provide acute treatment of a subjectsuffering from cardiac dysfunction, congestive heart failure, low renalblood flow, high renal vascular resistance, arterial hypertension,and/or kidney dysfunction. For example, the impeller may be placedinside the subject's renal veins for a period of more than one hour(e.g., more than one day), less than one week (e.g., less than fourdays), and/or between one hour and one week (e.g., between one day andfour days).

The pump is typically configured to pump blood in a downstream directionsuch as to reduce pressure in the renal vein. Typically, due to thereduction in pressure in the renal vein that is caused by the pumping ofthe blood in the downstream direction, perfusion of the kidneyincreases. In turn, this may cause pressure in the renal veins to riserelative to the pressure in the renal veins immediately subsequent toinitiation of the pumping, due to increased blood flow into the renalvein. Typically, even after perfusion of the kidney increases, the pumpis configured to maintain the pressure in the renal vein at a lowervalue than the pressure in the renal vein before the initiation of thepumping.

Typically, the subject's renal vein is protected from being injured bythe impeller, by placing a cage into the renal vein around the impeller,the cage separating a wall of the renal vein from the impeller. For someapplications, the cage and the impeller are engaged to one another by anengagement mechanism, such that, in response to the cage becomingradially compressed, the impeller becomes radially compressed and thecage thereby maintains a separation between the wall of the renal veinand the impeller.

In accordance with some applications, a pump and an occlusion element(e.g., a valve) are placed inside the subject's renal veins in order toprovide acute treatment of a subject suffering from cardiac dysfunction,congestive heart failure, low renal blood flow, high renal vascularresistance, arterial hypertension, and/or kidney dysfunction. Forexample, the pump and the occlusion element may be placed inside thesubject's renal veins for a period of more than one hour (e.g., morethan one day), less than one week (e.g., less than four days), and/orbetween one hour and one week (e.g., between one day and four days).

The occlusion element is configured to occlude the renal vein at anocclusion site. The pump is configured to pump blood in a downstreamdirection, from a site that is in fluid communication with the upstreamside of the occlusion element to a site that is in fluid communicationwith a downstream side of the occlusion element. In doing so, the pumpreduces pressure in the renal vein. The occlusion element is configuredto protect the renal vein from backflow of blood from the vena cava tothe renal vein.

Typically, due to the reduction in pressure in the renal vein that iscaused by the pumping of the blood in the downstream direction,perfusion of the kidney increases. In turn, this may cause pressure inthe renal veins to rise relative to the pressure in the renal veinsimmediately subsequent to initiation of the pumping, due to increasedblood flow into the renal vein. Typically, even after perfusion of thekidney increases, the pump is configured to maintain the pressure in therenal vein at a lower value than the pressure in the renal vein beforethe initiation of the pumping.

In accordance with some applications of the invention, ablood-impermeable sleeve is placed within the subject's vena cava suchthat a downstream end of the sleeve is coupled to the wall of the venacava at a first location that is downstream of all renal veins of thesubject, and such that an upstream end of the sleeve is coupled to awall of the vena cava at a second location that is upstream of all renalveins of the subject. Typically, a coupling structure, e.g., a rigidcoupling structure (such as a stent), is configured to couple theupstream and downstream ends of the sleeve to the vena cava.

A pump pumps blood from a location that is exterior to the sleeve to alocation that is in fluid communication with the interior of the sleeve(e.g., a location within the vena cava upstream or downstream of thesleeve). Thus, the pump pumps blood out of the subject's renal veins andinto the subject's vena cava. The sleeve prevents backflow of blood fromthe vena cava into the renal veins.

There is therefore provided, in accordance with some applications of thepresent invention, a method including:

identifying a subject as suffering from a condition selected from thegroup consisting of: cardiac dysfunction, congestive heart failure,reduced renal blood flow, increased renal vascular resistance, arterialhypertension, and kidney dysfunction; and

in response thereto, reducing blood pressure within a renal vein of thesubject, by placing an impeller inside the subject's renal vein andactivating the impeller to pump blood from the renal vein into a venacava of the subject.

For some applications, activating the impeller to pump blood from therenal vein into the vena cava includes enhancing a rate of blood flowfrom the renal vein into the vena cava, without causing a substantialchange in a direction of the blood flow relative to a direction of bloodflow from the renal vein into the vena cava in an absence of activatingthe pump.

For some applications, activating the impeller to pump blood from therenal vein into the vena cava includes activating the impeller to pumpblood from the renal vein directly into a portion of the vena cava thatis adjacent to the renal vein.

For some applications, activating the impeller to pump blood from therenal vein into the vena cava includes activating the impeller to pumpblood from the renal vein into the vena cava, without removing bloodfrom a venous system of the subject into a non-venous receptacle.

For some applications, placing the impeller inside the renal veinincludes protecting the subject's renal vein from being injured by theimpeller, by placing the impeller into the renal vein, with a cagedisposed around the impeller, the cage separating an inner wall of therenal vein from the impeller.

For some applications, placing the impeller into the renal vein with thecage disposed around the impeller includes placing the impeller into therenal vein, with the cage disposed around the impeller, the cage and theimpeller being engaged to one another by an engagement mechanism, suchthat in response to the cage becoming radially compressed, the impellerbecomes axially elongated such that the cage maintains a separationbetween the wall of the renal vein and the impeller.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   an impeller, including:        -   an impeller frame that includes proximal and distal end            portions and a plurality of helical elongate elements that            wind from the proximal end portion to the distal end            portion; and        -   a material that is coupled to the helical elongate elements,            such that the helical elongate elements with the material            coupled thereto define at least one blade of the impeller.

For some applications, the impeller includes a biocompatible impellerthat is configured to be inserted into a blood vessel of a subject.

For some applications, the plurality of elongate elements include aplurality of helical strips.

For some applications, at least one of the helical elongate elements hasa variable pitch, the pitch of the at least one of the elongate elementsvarying along a length of the helical elongate element.

For some applications, the impeller is configured to be placed inside ablood vessel of a subject and to pump blood through the blood vessel byrotating with respect to the blood vessel, the apparatus furtherincluding a radially expandable cage configured to be disposed betweenthe impeller and an inner wall of the blood vessel and to separate theblood vessel wall from the impeller.

For some applications, the proximal and distal end portions includesproximal and distal rings.

For some applications, at least one of the proximal and distal endportions defines a notch in an edge thereof, the notch being configuredto facilitate coupling of the material to the helical elongate elements.

For some applications, the impeller further includes sutures tied aroundthe helical elongate elements, the sutures being configured tofacilitate coupling of the material to the helical elongate elements.

For some applications, the plurality of helical elongate elementsincludes three helical elongate elements that wind from the proximal endportion to the distal end portion.

For some applications, when the impeller is in a non-constrainedconfiguration thereof, a length of each of the helical elongateelements, measured along a longitudinal axis of the impeller, is greaterthan 5 mm. For some applications, when the impeller is in thenon-constrained configuration thereof, the length of each of the helicalelongate elements, measured along a longitudinal axis of the impeller,is less than 14 mm.

For some applications, when the impeller is in a non-constrainedconfiguration thereof, a span of the impeller in a directionperpendicular to a longitudinal axis of the impeller is greater than 8mm. For some applications, the span of the impeller is greater than 10mm. For some applications, the span of the impeller is less than 15 mm.For some applications, the span of the impeller is less than 12 mm.

For some applications, the plurality of helical elongate elementsincludes two helical elongate elements that wind from the proximal endportion to the distal end portion.

For some applications, radii of each of the two helical elongateelements are within 20 percent of one another. For some applications,radii of each of the two helical elongate elements are similar to oneanother. For some applications, pitches of each of the two helicalelongate elements are within 20 percent of one another. For someapplications, pitches of each of the two helical elongate elements aresimilar to one another. For some applications, longitudinal axes of eachof the two helical elongate elements are parallel to each other andparallel to a longitudinal axis of the impeller.

For some applications, the material includes a continuous film ofmaterial that is supported by the helical elongate elements.

For some applications, each of the helical elongate elements definesmore than one eighth of a winding of a helix. For some applications,each of the helical elongate elements defines less than half a windingof a helix.

For some applications:

-   -   the helical elongate elements define proximal and distal ends        thereof,    -   the helical elongate elements are configured to support the        material between the proximal and distal ends of the helical        elongate elements, and    -   the impeller does not include any additional supporting member        for supporting the material between the proximal and distal ends        of the helical elongate elements.

For some applications, the impeller is configured such that rotationalmotion is imparted from the proximal end portion of the impeller to thedistal end portion of the impeller substantially solely via the helicalelongate elements of the impeller.

For some applications, the impeller, by not including any additionalsupporting member for supporting the material between the proximal anddistal ends of the helical elongate elements, is configured to beradially compressible to a smaller diameter than if the impeller were toinclude an additional supporting member for supporting the materialbetween the proximal and distal ends of the helical elongate elements.

For some applications, the impeller, by not including any additionalsupporting member for supporting the material between the proximal anddistal ends of the helical elongate elements, is configured to be moreflexible than if the impeller were to include an additional supportingmember for supporting the material between the proximal and distal endsof the helical elongate elements.

For some applications, the impeller, by not including any additionalsupporting member for supporting the material between the proximal anddistal ends of the helical elongate elements, is configured such that aforce that is required to axially elongate the impeller by a givenamount is less than would be required if the impeller were to include anadditional supporting member for supporting the material between theproximal and distal ends of the helical elongate elements.

There is additionally provided, in accordance with some applications ofthe present invention, a method, including:

-   -   manufacturing an impeller by:        -   cutting a tube such that the cut tube defines a structure            having first and second end portions at proximal and distal            ends of the structure, the end portions being connected to            one another by a plurality of elongate elements;        -   causing the elongate elements to radially expand and form            helical elongate elements, by axially compressing the            structure; and        -   coupling a material to the helical elongate elements, such            that the helical elongate elements with the material coupled            thereto define at least one blade of the impeller.

For some applications, cutting the tube includes laser cutting the tube.

For some applications, manufacturing the impeller includes manufacturinga biocompatible impeller that is configured to be inserted into a bloodvessel of a subject.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second endportions at proximal and distal ends of the structure, the end portionsbeing connected to one another by a plurality of strips.

For some applications, causing the elongate elements to radially expandand form helical elongate elements includes causing at least one of thehelical elongate elements to have a variable pitch, the pitch of the atleast one of the elongate elements varying along a length of the helicalelongate element.

For some applications, cutting the tube such that the cut tube defines astructure having first and second end portions at proximal and distalends of the structure includes cutting the tube such that the cut tubedefines a structure having first and second rings at proximal and distalends of the structure.

For some applications, cutting the tube further includes forming a notchin an edge of at least one of the end portions, the notch beingconfigured to facilitate coupling of the material to the helicalelongate elements.

For some applications, the method further includes tying sutures aroundthe helical elongate elements, the sutures being configured tofacilitate coupling of the material to the helical elongate elements.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second endportions at proximal and distal ends of the structure, the end portionsbeing connected to one another by three elongate elements, and causingthe elongate elements to radially expand and form helical elongateelements includes causing the elongate elements to form three helicalelongate elements.

For some applications, cutting the tube includes cutting the tube suchthat, in an absence of axial compression being applied to the structure,the structure has a length, measured along a longitudinal axis of thestructure, of greater than 15 mm. For some applications, cutting thetube includes cutting the tube such that, in the absence of axialcompression being applied to the structure, the length of the structure,measured along the longitudinal axis of the structure, is less than 25mm. For some applications, cutting the tube includes cutting the tubesuch that, in an absence of axial compression being applied to thestructure, each of the elongate elements has a length, measured along alongitudinal axis of the structure, of greater than 14 mm. For someapplications, cutting the tube includes cutting the tube such that, inthe absence of axial compression being applied to the structure, thelength of each of the elongate elements, measured along the longitudinalaxis of the structure, is less than 22 mm.

For some applications, axially compressing the structure includesaxially compressing the structure such that the structure defines alength, measured along a longitudinal axis of the structure, of greaterthan 8 mm. For some applications, axially compressing the structureincludes axially compressing the structure such that the length,measured along the longitudinal axis of the structure, is less than 18mm. For some applications, axially compressing the structure includesaxially compressing the structure such that each of the elongateelements defines a length, measured along a longitudinal axis of thestructure, of greater than 5 mm. For some applications, axiallycompressing the structure includes axially compressing the structuresuch that the length of each of the elongate elements, measured alongthe longitudinal axis of the structure, is less than 14 mm.

For some applications, axially compressing the structure includesaxially compressing the structure such that a span of the structure in adirection perpendicular to a longitudinal axis of the structure isgreater than 8 mm. For some applications, axially compressing thestructure includes axially compressing the structure such that the spanof the structure is greater than 10 mm. For some applications, axiallycompressing the structure includes axially compressing the structuresuch that the span of the structure is less than 15 mm. For someapplications, axially compressing the structure includes axiallycompressing the structure such that the span of the structure is lessthan 12 mm.

For some applications, coupling the material to the helical elongateelements includes dipping at least a portion of the structure into thematerial, while the material is in a liquid state thereof, and dryingthe material, while the material is being supported by the helicalelongate elements. For some applications, drying the material includescuring the material.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second endportions at proximal and distal ends of the structure, the end portionsbeing connected to one another by two elongate elements, and causing theelongate elements to radially expand and form helical elongate elementsincludes causing the elongate elements to form two helical elongateelements.

For some applications, drying the liquid material while the material isbeing supported by the helical elongate elements includes causing thematerial to form a continuous film between the helical elongateelements, the continuous film being supported by the helical elongateelements.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second endportions at proximal and distal ends of the structure, the end portionsbeing connected to one another by two elongate elements, and causing theelongate elements to radially expand and form helical elongate elementsincludes causing the elongate elements to form two helical elongateelements.

For some applications, causing the elongate elements to form the twohelical elongate elements includes causing the elongate elements to formtwo helical elongate elements both of which originate at the first endportion, and terminate at the second end portion, radii of the helicalelongate elements being similar to one another. For some applications,causing the elongate elements to form the two helical elongate elementsincludes causing the elongate elements to form two helical elongateelements both of which originate at the first end portion, and terminateat the second end portion, radii of the helical elongate elements beingwithin 20 percent of one another.

For some applications, causing the elongate elements to form the twohelical elongate elements includes causing the elongate elements to formtwo helical elongate elements both of which originate at the first endportion, and terminate at the second end portion, pitches of the helicalelongate elements being similar to one another. For some applications,causing the elongate elements to form the two helical elongate elementsincludes causing the elongate elements to form two helical elongateelements both of which originate at the first end portion, and terminateat the second end portion, pitches of the helical elongate elementsbeing within 20 percent of one another.

For some applications, causing the elongate elements to form the twohelical elongate elements includes causing the elongate elements to formtwo helical elongate elements, longitudinal axes of both of the helicalelongate elements being parallel to each other and parallel to alongitudinal axis of the impeller.

For some applications, causing the elongate elements to form the twohelical elongate elements includes causing the elongate elements to formtwo helical elongate elements, each of the helical elongate elementsdefining more than one eighth of a winding of a helix. For someapplications, causing the elongate elements to form the two helicalelongate elements includes causing the elongate elements to form twohelical elongate elements, each of the helical elongate elementsdefining less than half a winding of a helix.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second rings atproximal and distal ends of the structure, and such that first andsecond ends of each of the elongate elements are disposed at an anglefrom one another with respect to circumferences of the rings, the anglebeing greater than 50 degrees. For some applications, cutting the tubeincludes cutting the tube such that the first and second ends of each ofthe elongate elements are disposed at an angle from one another withrespect to circumferences of the rings, the angle being greater than 70degrees. For some applications, cutting the tube includes cutting thetube such that the first and second ends of each of the elongateelements are disposed at an angle from one another with respect tocircumferences of the rings, the angle being greater than 90 degrees.

For some applications, cutting the tube includes cutting the tube suchthat the cut tube defines a structure having first and second rings atproximal and distal ends of the structure, and such that first andsecond ends of each of the elongate elements are disposed at an anglefrom one another with respect to circumferences of the rings, the anglebeing less than 180 degrees. For some applications, cutting the tubeincludes cutting the tube such that the first and second ends of each ofthe elongate elements are disposed at an angle from one another withrespect to circumferences of the rings, the angle being less than 150degrees. For some applications, cutting the tube includes cutting thetube such that the first and second ends of each of the elongateelements are disposed at an angle from one another with respect tocircumferences of the rings, the angle being less than 110 degrees.

For some applications, coupling the material to the helical elongateelements includes coupling the material to the elongate elements suchthat, between the proximal and distal ends of the helical elongateelements, the material is supported by the helical elongate elements, inan absence of any additional supporting member between the proximal anddistal ends of the helical elongate elements for supporting thematerial.

For some applications, coupling the material to the helical elongateelements in the absence of any additional supporting member between theproximal and distal ends of the helical elongate elements for supportingthe material includes configuring the impeller such that rotationalmotion is imparted from the proximal end portion to the distal endportion substantially solely via the helical elongate elements of theimpeller.

For some applications, coupling the material to the helical elongateelements in the absence of any additional supporting member between theproximal and distal ends of the helical elongate elements for supportingthe material includes configuring the impeller to be radiallycompressible to a smaller diameter than if the impeller were to includean additional supporting member for supporting the material between theproximal and distal ends of the helical elongate elements.

For some applications, coupling the material to the helical elongateelements in the absence of any additional supporting member between theproximal and distal ends of the helical elongate elements for supportingthe material includes configuring the impeller to be more flexible thanif the impeller were to include an additional supporting member forsupporting the material between the proximal and distal ends of thehelical elongate elements.

For some applications, coupling the material to the helical elongateelements in the absence of any additional supporting member between theproximal and distal ends of the helical elongate elements for supportingthe material includes configuring the impeller such that a force that isrequired to axially elongate the impeller by a given amount is less thanwould be required if the impeller were to include an additionalsupporting member for supporting the material between the proximal anddistal ends of the helical elongate elements.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   an impeller configured, in a radially-expanded configuration        thereof, to pump a fluid by rotating;    -   a radially expandable cage disposed around the impeller, such        that, in radially-expanded configurations of the impeller and        the cage, the impeller is separated from an inner surface of the        cage; and    -   an engagement mechanism configured to engage the impeller with        respect to the cage, such that, in response to the cage becoming        radially compressed, the engagement mechanism axially elongates        the impeller such that the impeller remains separated from the        inner surface of the cage.

For some applications:

-   -   the cage and the impeller define axially-elongated        configurations thereof, the cage, while in its axially-elongated        configuration, being configured to accommodate the impeller        inside the cage, while the impeller is in its axially-elongated        configuration, and    -   the cage includes struts, at least some of the struts including        portions thereof that are undulated at least when the cage is in        the radially-expanded configuration of the cage,    -   a level of undulation of the undulated portions of the struts        when the cage is in its radially-expanded configuration being        greater than a level of undulation of the undulated portions of        the struts when the cage is in its axially-elongated        configuration.

For some applications, the engagement mechanism is configured to permitrotation of the impeller, while the cage is maintained in a rotationallyfixed position.

For some applications, the engagement mechanism is configured, inresponse to the cage becoming radially compressed, to axially elongatethe impeller, by imparting to the impeller longitudinal motion that iscaused by longitudinal motion of the cage.

For some applications, the impeller includes a biocompatible impellerthat is configured to be placed inside a blood vessel and to pump bloodthrough the blood vessel by rotating, and the cage is configured to bedisposed between the impeller and an inner wall of the blood vessel andto separate the blood vessel wall from the impeller.

For some applications, the cage includes struts that are shaped todefine cells, and the cage is configured to separate the blood vesselwall from the impeller even if the blood vessel wall protrudes through acell of the cage.

For some applications:

-   -   the impeller is coupled to the cage such that a longitudinal        axis of the impeller is aligned with a longitudinal axis of the        cage, and    -   the cage defines a central portion thereof that has a generally        cylindrical shape, an outer surface of the cage at the generally        cylindrical portion of the cage being parallel to the        longitudinal axis of the cage.

For some applications, the impeller is configured to be placed inside ablood vessel and to pump blood through the blood vessel by rotating, andthe cage is configured to be disposed between the impeller and an innerwall of the blood vessel and to separate the inner wall of the bloodvessel from the impeller.

For some applications, the cage is configured to radially expand insidethe blood vessel such that the outer surface of the cage at thegenerally cylindrical portion of the cage engages the inner wall of theblood vessel, the cage thereby becoming oriented within the blood vesselsuch that the longitudinal axis of the cage is parallel to a locallongitudinal axis of the blood vessel.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   placing inside a blood vessel of a subject:        -   an impeller configured, in a radially-expanded configuration            thereof, to pump blood through the blood vessel by rotating;            and        -   a radially-expandable cage disposed around the impeller;    -   radially expanding the cage and the impeller inside the blood        vessel, such that the impeller is separated from an inner wall        of the blood vessel by the cage,        -   the impeller being engaged with respect to the cage, such            that, in response to the cage becoming radially compressed,            the impeller is axially elongated, such    -   that the impeller remains separated from the inner wall of the        blood vessel; and    -   operating a control unit to pump blood through the blood vessel        by rotating the impeller.

For some applications, the blood vessel includes a renal vein, andoperating the control unit to pump blood through the blood vesselincludes operating the control unit to pump blood away from a kidney ofthe subject toward a vena cava of the subject.

For some applications, the method further includes operating the controlunit to:

-   -   measure pressure within the subject's blood vessel at a first        location within the blood vessel that is upstream of the        impeller, and at a second location within the blood vessel that        is downstream of the impeller; and    -   control rotation of the impeller responsively to the pressure        measured at the first and second locations.

For some applications:

-   -   placing the cage and the impeller inside the blood vessel        includes placing the cage and the impeller inside the blood        vessel while the cage and the impeller are in axially-elongated        configurations thereof, and while the cage, while in its        axially-elongated configuration accommodates the impeller inside        the cage, while the impeller is in its axially-elongated        configuration,    -   the cage includes a cage that defines struts, at least some of        the struts including portions thereof that are undulated at        least when the cage is in a radially-expanded configuration, and    -   radially expanding the cage includes radially expanding the cage        such that a level of undulation of the undulated portions of the        struts becomes greater than a level of undulation of the        undulated portions of the struts when the cage was in its        axially-elongated configuration.

For some applications, operating the control unit to rotate the impellerincludes operating the control unit to rotate the impeller, while thecage is maintained in a rotationally fixed position.

For some applications, the cage includes struts that are shaped todefine cells, and radially expanding the cage includes separating theblood vessel wall from the impeller even if the blood vessel wallprotrudes through a cell of the cage, by radially expanding the cage.

For some applications:

-   -   placing the impeller and the cage inside the blood vessel        includes placing the impeller and the cage inside the blood        vessel, the impeller being coupled to the cage such that a        longitudinal axis of the impeller is aligned with a longitudinal        axis of the cage,    -   the cage includes a cage that defines a central portion thereof        that has a generally cylindrical shape, an outer surface of the        cage at the generally cylindrical portion of the cage being        parallel to the longitudinal axis of the cage, and    -   radially expanding the cage inside the blood vessel includes        radially expanding the cage inside the blood vessel such that        the outer surface of the cage at the generally cylindrical        portion of the cage engages the inner wall of the blood vessel,        the cage thereby becoming oriented within the blood vessel such        that a longitudinal axis of the cage is parallel to a local        longitudinal axis of the blood vessel.

For some applications:

-   -   the blood vessel has a given diameter in an absence of the cage;    -   radially expanding the cage includes widening a portion of the        blood vessel such that a diameter of the portion of the blood        vessel is greater than the given diameter; and    -   radially expanding the impeller includes radially expanding the        impeller such that a span of the impeller is at least equal to        the given diameter.

For some applications, the method further includes operating the controlunit to:

-   -   measure flow through the blood vessel; and    -   control rotation of the impeller responsively to the measured        flow.

For some applications, operating the control unit to measure flowthrough the blood vessel includes operating the control unit to measureblood flow via a thermal flow sensor that is disposed within a housing,the housing being configured such that blood flow through the housing issubstantially in a direction parallel to a local longitudinal axis ofthe blood vessel.

There is further provided, in accordance with some applications of thepresent invention apparatus including:

-   -   a radially-expandable impeller configured, in a        radially-expanded configuration thereof, to pump a fluid by        rotating;    -   a radially-expandable cage disposed around the impeller, such        that, in radially-expanded configurations of the impeller and        the cage, the impeller is separated from an inner surface of the        cage;    -   the impeller being coupled to the cage such that a longitudinal        axis of the impeller is aligned with a longitudinal axis of the        cage, and    -   the cage defining a central portion thereof that has a generally        cylindrical shape, an outer surface of the cage at the generally        cylindrical portion of the cage being parallel to the        longitudinal axis of the cage.

For some applications:

-   -   the cage and the impeller define axially-elongated        configurations thereof, the cage, while in its axially-elongated        configuration, being configured to accommodate the impeller        inside the cage, while the impeller is in its axially-elongated        configuration, and    -   the cage includes struts, at least some of the struts including        portions thereof that are undulated at least when the cage is in        the radially-expanded configuration of the cage,    -   a level of undulation of the undulated portions of the struts        when the cage is in its radially-expanded configuration being        greater than a level of undulation of the undulated portions of        the struts when the cage is in its axially-elongated        configuration.

For some applications:

-   -   the impeller defines proximal and distal rings, respectively, at        proximal and distal ends thereof,    -   the cage defines proximal and distal rings, respectively, at        proximal and distal ends thereof,    -   the impeller is coupled to the cage such that the longitudinal        axis of the impeller is aligned with the longitudinal axis of        the cage by:        -   the proximal rings of the impeller and the cage being placed            on a first support element such that the proximal rings of            the impeller and the cage are aligned with one another, and        -   the distal rings of the impeller and the cage being placed            on a second support element such that the distal rings of            the impeller and the cage are aligned with one another.

For some applications, the apparatus further includes an engagementmechanism configured to engage the impeller with respect to the cage,such that, in response to the cage becoming radially compressed, theengagement mechanism axially elongates the impeller such that theimpeller remains separated from the inner surface of the cage.

For some applications, the engagement mechanism is configured to permitrotation of the impeller, while the cage is maintained in a rotationallyfixed position.

For some applications, the engagement mechanism is configured, inresponse to the cage becoming radially compressed, to axially elongatethe impeller, by imparting to the impeller longitudinal motion that iscaused by longitudinal motion of the cage.

For some applications, the impeller is a biocompatible impeller that isconfigured to be placed inside a blood vessel and to pump blood throughthe blood vessel by rotating, and the cage is configured to be disposedbetween the impeller and an inner wall of the blood vessel and toseparate the blood vessel wall from the impeller.

For some applications, the cage includes struts that are shaped todefine cells, and the cage is configured to separate the blood vesselwall from the impeller even if the blood vessel wall protrudes through acell of the cage.

For some applications, the impeller is a biocompatible impeller that isconfigured to be placed inside a blood vessel and to pump blood throughthe blood vessel by rotating, and the cage is configured to be disposedbetween the impeller and an inner wall of the blood vessel and toseparate the blood vessel wall from the impeller.

For some applications, the cage is configured to radially expand insidethe blood vessel such that the outer surface of the cage at thegenerally cylindrical portion of the cage engages the inner wall of theblood vessel, the cage thereby becoming oriented within the blood vesselsuch that the longitudinal axis of the cage is parallel to a locallongitudinal axis of the blood vessel.

There is further provided, in accordance with some applications of thepresent invention, a method including:

-   -   placing inside a blood vessel of a subject:        -   an impeller configured, in a radially-expanded configuration            thereof, to pump blood through the blood vessel by rotating;        -   a radially-expandable cage disposed around the impeller, the            impeller being coupled to the cage such that a longitudinal            axis of the impeller is aligned with a longitudinal axis of            the cage, and the cage defining a central portion thereof            that has a generally cylindrical shape, an outer surface of            the cage at the generally cylindrical portion of the cage            being parallel to the longitudinal axis of the cage;    -   radially expanding the cage and the impeller inside the blood        vessel, such that:        -   the impeller is separated from an inner wall of the blood            vessel by the cage, and    -   the outer surface of the cage at the generally cylindrical        portion of the cage engages the inner wall of the blood vessel,        the cage thereby becoming oriented within the blood vessel such        that a longitudinal axis of the cage is parallel to a local        longitudinal axis of the blood vessel; and    -   operating a control unit to pump blood through the blood vessel        by rotating the impeller.

For some applications, the method further includes operating the controlunit to:

-   -   measure pressure within the subject's blood vessel at a first        location within the blood vessel that is upstream of the        impeller, and at a second location within the blood vessel that        is downstream of the impeller; and    -   control rotation of the impeller responsively to the pressure        measured at the first and second locations.

For some applications:

-   -   the blood vessel has a given diameter in an absence of the cage;    -   radially expanding the cage includes widening a portion of the        blood vessel such that a diameter of the portion of the blood        vessel is greater than the given diameter; and    -   radially expanding the impeller includes radially expanding the        impeller such that a span of the impeller is at least equal to        the given diameter.

For some applications, the method further includes operating the controlunit to:

-   -   measure flow through the blood vessel; and    -   control rotation of the impeller responsively to the measured        flow.

For some applications, operating the control unit to measure flowthrough the blood vessel includes operating the control unit to measureblood flow via a thermal flow sensor that is disposed within a housing,the housing being configured such that blood flow through the housing issubstantially in a direction parallel to the local longitudinal axis ofthe blood vessel.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a radially-expandable impeller configured, in a        radially-expanded configuration thereof, to pump a fluid by        rotating; and    -   a radially-expandable cage disposed around the impeller, such        that, in radially-expanded configurations of the impeller and        the cage, the impeller is separated from an inner surface of the        cage,        -   the cage and the impeller defining axially-elongated            configurations thereof, the cage, while in its            axially-elongated configuration, being configured to            accommodate the impeller inside the cage, while the impeller            is in its axially-elongated configuration,        -   the cage including struts, at least some of the struts            including portions thereof that are undulated at least when            the cage is in the radially-expanded configuration of the            cage,        -   a level of undulation of the undulated portions of the            struts when the cage is in its radially-expanded            configuration, being greater than a level of undulation of            the undulated portions of the struts when the cage is in its            axially-elongated configuration.

For some applications, for each of the struts that include the undulatedportions, the strut is configured such that a ratio of:

-   -   a shortest distance from a first longitudinal end of the strut        to a second longitudinal end of the strut when the cage is its        axially-elongated configuration, to    -   a shortest distance from the first longitudinal end of the strut        to the second longitudinal end of the strut when the cage is its        radially-expanded configuration,    -   is greater than 1.05:1.

For some applications, the ratio is less than 1.4:1. For someapplications, the ratio is greater than 1.15:1. For some applications,the ratio is greater than 1.2:1.

For some applications, the apparatus further includes an engagementmechanism configured to engage the impeller with respect to the cage,such that, in response to the cage becoming axially elongated, theimpeller is axially elongated such that the impeller remains separatedfrom the inner surface of the cage.

For some applications, the engagement mechanism is configured to permitrotation of the impeller, while the cage is maintained in a rotationallyfixed position.

For some applications, the engagement mechanism is configured, inresponse to the cage becoming axially elongated, to axially elongate theimpeller, by imparting to the impeller longitudinal motion that iscaused by longitudinal motion of the cage.

For some applications:

-   -   the cage and the impeller are biocompatible and are configured        to be inserted into a blood vessel, while the impeller is        disposed inside the cage, and while the cage and the impeller        are in the axially-elongated configurations thereof,    -   the impeller is configured to radially expand inside the blood        vessel and to pump blood through the blood vessel by rotating,        and    -   the cage is configured to radially expand inside the blood        vessel and to be disposed between the impeller and an inner wall        of the blood vessel such as to separate the inner wall of the        blood vessel from the impeller.

For some applications, the struts of the cage are shaped to definecells, and the cage is configured to separate the blood vessel wall fromthe impeller even if the blood vessel wall protrudes through a cell ofthe cage.

For some applications:

-   -   the impeller is coupled to the cage such that a longitudinal        axis of the impeller is aligned with a longitudinal axis of the        cage, and    -   the cage defines a central portion thereof that has a generally        cylindrical shape, an outer surface of the cage at the generally        cylindrical portion of the cage being parallel to the        longitudinal axis of the cage.

For some applications, the impeller is biocompatible and is configuredto be placed inside a blood vessel and to pump blood through the bloodvessel by rotating, and the cage is configured to be disposed betweenthe impeller and an inner wall of the blood vessel and to separate theinner wall of the blood vessel from the impeller.

For some applications, the cage is configured to radially expand insidethe blood vessel such that the outer surface of the cage at thegenerally cylindrical portion of the cage engages the inner wall of theblood vessel, the cage thereby becoming oriented within the blood vesselsuch that the longitudinal axis of the cage is parallel to a locallongitudinal axis of the blood vessel.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   placing inside a blood vessel of a subject:        -   an impeller configured, in a radially-expanded configuration            thereof, to pump blood through the blood vessel by rotating;            and        -   a radially-expandable cage disposed around the impeller, the            cage defining struts,            -   the placing being performed while the cage and the                impeller are in axially-elongated configurations                thereof, and while the cage, while in its                axially-elongated configuration, accommodates the                impeller inside the cage, while the impeller is in its                axially-elongated configuration;    -   radially expanding the cage and the impeller inside the blood        vessel, such that the cage and the impeller are in        radially-expanded configurations thereof, and such that the        impeller is separated from an inner wall of the blood vessel by        the cage; and    -   operating a control unit to pump blood through the blood vessel        by rotating the impeller,        -   the cage including struts, at least some of the struts            including portions thereof that are undulated at least when            the cage is in the radially-expanded configuration of the            cage,        -   radially expanding the cage including radially expanding the            cage such that a level of undulation of the undulated            portions of the struts becomes greater than a level of            undulation of the undulated portions of the struts when the            cage was in its axially-elongated configuration.

For some applications, the blood vessel includes a renal vein, andoperating the control unit to pump blood through the blood vesselincludes operating the control unit to pump blood away from a kidney ofthe subject toward a vena cava of the subject.

For some applications, the method further includes operating the controlunit to:

-   -   measure pressure within the subject's blood vessel at a first        location within the blood vessel that is upstream of the        impeller, and at a second location within the blood vessel that        is downstream of the impeller; and    -   control rotation of the impeller responsively to the pressure        measured at the first and second locations.

For some applications:

-   -   the blood vessel has a given diameter in an absence of the cage;    -   radially expanding the cage includes widening a portion of the        blood vessel such that a diameter of the portion of the blood        vessel is greater than the given diameter; and    -   radially expanding the impeller includes radially expanding the        impeller such that a span of the impeller is at least equal to        the given diameter.

For some applications, radially expanding the cage includes radiallyexpanding the cage such that, for each of the struts that include theundulated portions, a ratio of:

-   -   a shortest distance from a first longitudinal end of the strut        to a second longitudinal end of the strut when the cage is its        axially-elongated configuration, to    -   a shortest distance from the first longitudinal end of the strut        to the second longitudinal end of the strut when the cage is its        radially-expanded configuration,    -   is greater than 1.05:1.

For some applications, radially expanding the cage includes radiallyexpanding the cage such that, for each of the struts that include theundulated portions, the ratio is less than 1.4:1. For some applications,radially expanding the cage includes radially expanding the cage suchthat, for each of the struts that include the undulated portions, theratio is greater than 1.15:1. For some applications, radially expandingthe cage includes radially expanding the cage such that, for each of thestruts that include the undulated portions, the ratio is greater than1.2:1.

For some applications, the method further includes operating the controlunit to:

-   -   measure flow through the blood vessel; and    -   control rotation of the impeller responsively to the measured        flow.

For some applications, operating the control unit to measure flowthrough the blood vessel includes operating the control unit to measureblood flow via a thermal flow sensor that is disposed within a housing,the housing being configured such that blood flow through the housing issubstantially in a direction parallel to a local longitudinal axis ofthe blood vessel.

There is further provided in accordance with some applications of thepresent invention, a method including:

-   -   placing a radially expandable structure inside a blood vessel of        a subject, the blood vessel having a given diameter in an        absence of the radially expandable structure;    -   widening a portion of the blood vessel such that a diameter of        the portion of the blood vessel is greater than the given        diameter, by expanding the radially expandable structure inside        the portion of the blood vessel;    -   placing an impeller inside the portion of the blood vessel, the        impeller including impeller blades, a span of the impeller        blades being at least equal to the given diameter; and    -   operating a control unit to pump blood through the blood vessel        by rotating the impeller with respect to the blood vessel.

For some applications, expanding the radially-expandable structureincludes expanding a radially-expandable cage that is disposed aroundthe impeller such that the impeller is separated from an inner wall ofthe blood vessel by the cage.

For some applications, the blood vessel includes a renal vein, andoperating the control unit to pump blood through the blood vesselincludes operating the control unit to pump blood away from a kidney ofthe subject toward a vena cava of the subject.

For some applications, the method further includes operating the controlunit to:

-   -   measure pressure within the subject's blood vessel at a first        location within the blood vessel that is upstream of the        impeller, and at a second location within the blood vessel that        is downstream of the impeller; and    -   control rotation of the impeller responsively to the pressure        measured at the first and second locations.

For some applications, the method further includes operating the controlunit to:

-   -   measure flow through the blood vessel; and    -   control rotation of the impeller responsively to the measured        flow.

For some applications, operating the control unit to measure flowthrough the blood vessel includes operating the control unit to measureblood flow via a thermal flow sensor that is disposed within a housing,the housing being configured such that blood flow through the housing issubstantially in a direction parallel to a local longitudinal axis ofthe blood vessel.

For some applications, widening the portion of the blood vessel includeswidening the portion of the blood vessel such that the diameter of theportion of the blood vessel is greater than 105 percent of the givendiameter, by expanding the radially expandable structure inside theportion of the blood vessel. For some applications, widening the portionof the blood vessel includes widening the portion of the blood vesselsuch that the diameter of the portion of the blood vessel is greaterthan 115 percent of the given diameter, by expanding the radiallyexpandable structure inside the portion of the blood vessel. For someapplications, widening the portion of the blood vessel includes wideningthe portion of the blood vessel such that the diameter of the portion ofthe blood vessel is less than 125 percent of the given diameter, byexpanding the radially expandable structure inside the portion of theblood vessel.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a blood pump configured to pump blood through a blood vessel of        a subject, the blood pump including:        -   an elongate element; and        -   an impeller disposed at a distal end of the elongate            element, and configured to pump blood through the blood            vessel by rotating;    -   a thermal flow sensor configured to measure flow of the pumped        blood, the thermal flow sensor including an upstream temperature        sensor, a heating element and a downstream temperature sensor,        disposed sequentially along a portion of a length of the        elongate element,    -   the elongate element including a housing that is configured to        house the thermal flow sensor, and that is configured such that        blood flow through the housing is substantially in a direction        parallel to a local longitudinal axis of the blood vessel.

For some applications, the housing includes a portion of an outersurface of the elongate element that is shaped to define an indentationtherein, and the upstream temperature sensor, the heating element, andthe downstream temperature sensor are disposed sequentially along theindentation.

For some applications, a ratio of a length of the indentation to a widthof the indentation is greater than 4:1.

For some applications, the apparatus further includes a cover coupled tothe elongate element and disposed such as to cover the thermal sensor.

For some applications, the housing includes a housing disposed on anouter surface of the elongate element, and the upstream temperaturesensor, the heating element, and the downstream temperature sensor aredisposed sequentially along an inside of the housing.

For some applications, the housing includes a compressible tube disposedon the outer surface of the elongate element.

For some applications, a ratio of a length of the housing to a width ofthe housing is greater than 4:1. For some applications, a ratio of thelength of the housing to a height of the housing is greater than 4:1.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   placing into a blood vessel of a subject a blood pump that        includes:        -   an elongate element; and        -   an impeller disposed at a distal end of the elongate            element;    -   operating a control unit to measure flow of the pumped blood,        using a thermal flow sensor that includes an upstream        temperature sensor, a heating element, and a downstream        temperature sensor disposed sequentially along a portion of a        length of the elongate element,        -   the elongate element including a housing that is configured            to house the thermal flow sensor, and that is configured            such that blood flow through the housing is substantially in            a direction parallel to a local longitudinal axis of the            blood vessel; and    -   operating the control unit to pump blood through the blood        vessel by rotating the impeller, at least partially in response        to the measured flow.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a pump configured to pump a fluid including:        -   an elongate element; and        -   an impeller disposed at a distal end of the elongate            element, and configured to pump the fluid by rotating;    -   a thermal flow sensor configured to measure flow of the pumped        fluid, the thermal flow sensor including an upstream temperature        sensor, a heating element, and a downstream temperature sensor        disposed sequentially along a portion of a length of the        elongate element,    -   the elongate element including a housing that is configured to        house the thermal flow sensor, and that is configured such that        flow of the fluid through the housing is substantially in a        direction parallel to a local longitudinal axis of the elongate        element.

For some applications, the housing includes a portion of an outersurface of the elongate element that is shaped to define an indentationtherein, and the upstream temperature sensor, the heating element, andthe downstream temperature sensor are disposed sequentially along theindentation.

For some applications, a ratio of a length of the indentation to a widthof the indentation is greater than 4:1.

For some applications, the apparatus further includes a cover coupled tothe elongate element and disposed such as to cover the thermal sensor.

For some applications, the housing includes a housing disposed on anouter surface of the elongate element, and the upstream temperaturesensor, the heating element, and the downstream temperature sensor aredisposed sequentially along an inside of the housing.

For some applications, the housing includes a compressible tube disposedon the outer surface of the elongate element.

For some applications, a ratio of a length of the housing to a width ofthe housing is greater than 4:1. For some applications, a ratio of thelength of the housing to a height of the housing is greater than 4:1.

There is further provided, in accordance with some applications of thepresent invention, a method for use with a plurality of tributary veinsthat supply a main vein, including:

-   -   mechanically isolating blood within the plurality of veins into        a compartment that is separated from blood flow within the main        vein; and    -   controlling blood flow from the plurality of veins to the major        vein by pumping blood from the compartment to the main vein.

For some applications, the method further includes performingultrafiltration on the pumped blood.

For some applications,

-   -   isolating the plurality of veins includes:        -   placing into the main vein a blood-impermeable sleeve and a            helical support element disposed around the sleeve, and        -   coupling the sleeve to a wall of the main vein using the            helical support element; and    -   pumping blood from the compartment to the main vein includes        guiding a distal portion of a blood pump into the compartment        using the helical support element and pumping the blood using        the blood pump.

For some applications:

-   -   isolating the plurality of veins includes:        -   placing into the main vein a blood-impermeable sleeve and a            helical portion of a blood pump that is disposed around the            sleeve and configured to support the sleeve, and        -   coupling the sleeve to a wall of the main vein; and    -   pumping blood from the compartment to the main vein includes        pumping blood into inlet holes of the blood pump that are        defined by the helical portion of the blood pump.

For some applications:

-   -   isolating blood within the plurality of veins into a compartment        that is separated from blood flow within the main vein includes        isolating blood in renal veins of the subject into a compartment        that is separated from blood flow within a vena cava of the        subject by placing a blood-impermeable sleeve in the subject's        vena cava, such that a downstream end of the sleeve is coupled        to a wall of the vena cava at a first location that is        downstream of all of the renal veins of the subject, and such        that an upstream end of the sleeve is coupled to the wall of the        vena cava at a second location that is upstream of all the renal        veins of the subject; and    -   pumping blood from the compartment to the main vein includes        operating a pump to pump blood from the compartment to a        location that is in fluid communication with an interior of the        sleeve.

For some applications, pumping blood from the compartment includesdrawing blood in a downstream direction through the renal veins.

For some applications, placing the sleeve in the vena cava includesplacing the sleeve in the vena cava for less than one week, andoperating the pump includes operating the pump for less than one week.

For some applications, the method further includes identifying thesubject as a subject suffering from a condition selected from the groupconsisting of: cardiac dysfunction, congestive heart failure, reducedrenal blood flow, increased renal vascular resistance, arterialhypertension, and kidney dysfunction, and operating the pump includes,in response to identifying the subject as suffering from the condition,reducing blood pressure within the subject's renal veins by operatingthe pump.

For some applications, placing the sleeve in the subject's vena cavaincludes anchoring the sleeve to the vena cava by causing the vena cavato constrict around at least a portion of the sleeve, by operating thepump.

For some applications, operating the pump to pump blood from thecompartment to the location that is in fluid communication with aninterior of the sleeve includes operating the pump to pump blood fromthe compartment to a site of the vena cava that is upstream of thesleeve.

For some applications, operating the pump to pump blood from thecompartment to the location that is in fluid communication with aninterior of the sleeve includes operating the pump to pump blood fromthe compartment to a site of the vena cava that is downstream of thesleeve.

For some applications, placing the sleeve in the vena cava includesplacing into the vena cava:

-   -   a stent shaped to define widened upstream and downstream ends        thereof that are widened relative to a central portion of the        stent, and    -   a blood-impermeable sleeve coupled to the stent, the sleeve        defining flared upstream and downstream ends thereof that are        coupled, respectively, to the widened upstream and downstream        ends of the stent; and    -   coupling the stent to the blood vessel such that:        -   in response to blood pressure on a first side of at least            one of the flared ends of the sleeve being greater than            blood pressure on a second side of the at least one flared            end of the sleeve, blood flows between an outside of the at            least one flared end of the sleeve and an inner wall of the            blood vessel, and        -   in response to blood pressure on the first side of the at            least one flared end of the sleeve being less than blood            pressure on the second side of the at least one flared end            of the sleeve, the at least one flared end of the sleeve            occludes blood flow between the outside of the at least one            flared end of the sleeve and the inner wall of the blood            vessel by contacting the inner wall of the blood vessel.

For some applications, placing the sleeve in the vena cava includesplacing into the vena cava:

-   -   a sleeve that is shaped to define flared ends thereof, and a        narrow central portion between the flared ends, and    -   a stent shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.

For some applications, pumping blood from the compartment includespumping blood from a site between an outside of the sleeve and an innerwall of the vena cava.

For some applications, the method further includes inserting the pumpinto the compartment via an opening in the sleeve through which the pumpis insertable.

For some applications, inserting the pump through the opening includesinserting the pump through an opening having a diameter that is between2 mm and 10 mm.

For some applications, inserting the pump through the opening includesinserting the pump through the opening such that the opening forms aseal around the pump.

For some applications, the method further includes inserting the pumpinto the compartment via a pump-accommodating sleeve that protrudes fromthe sleeve.

For some applications, inserting the pump into the compartment via thepump-accommodating sleeve includes inserting the pump into thecompartment via a pump-accommodating sleeve having a diameter that isbetween 2 mm and 10 mm.

For some applications, inserting the pump into the compartment via thepump-accommodating sleeve includes inserting the pump into thecompartment via the pump-accommodating sleeve such that thepump-accommodating sleeve forms a seal around the pump.

There is further provided, in accordance with some applications of thepresent invention, apparatus, including:

-   -   a blood-impermeable sleeve;    -   at least one support structure configured to couple first and        second ends of the sleeve to a blood vessel of a subject; and

a pump configured to pump blood from an exterior of the sleeve to alocation that is in fluid communication with an interior of the sleeve.

For some applications, the pump is configured to perform ultrafiltrationon the blood.

For some applications, the pump is configured to anchor the structure tothe blood vessel by causing the blood vessel to constrict around atleast a portion of the structure.

For some applications,

the structure includes a stent shaped to define widened ends thereofthat are widened relative to a central portion of the stent, and

-   -   the sleeve includes a sleeve that is coupled to the stent,        -   the sleeve defining flared ends thereof that are coupled to            the widened ends of the stent,        -   at least one of the flared ends of the sleeve being            configured to act as a valve by at least partially            separating from widened end of the stent to which it is            coupled in response to pressure being applied to the flared            end of the sleeve.

For some applications:

-   -   the support structure includes a helical support element        disposed around the sleeve, and    -   a distal portion of the blood pump is configured to be guided        such as to be disposed around the exterior of the sleeve using        the helical support element.

For some applications:

-   -   the support structure includes a helical portion of the blood        pump that is disposed around the sleeve and configured to        support the sleeve, and    -   the pump is configured to pump blood from the exterior of the        sleeve by pumping blood into inlet holes of the pump that are        defined by the helical portion of the blood pump.

For some applications:

-   -   the sleeve is shaped to define flared ends thereof, and a narrow        central portion between the flared ends;    -   the structure includes a stent shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.

For some applications, the pump is configured to pump blood from a sitebetween an outside of the sleeve and an inner wall of the blood vesselby being placed between the outside of the sleeve and thevessel-wall-supporting frame.

For some applications, the structure is configured to isolate blood in arenal vein of the subject into a compartment that is separated fromblood flow within a vena cava of the subject, by coupling a downstreamend of the sleeve to a wall of the vena cava at a first location that isdownstream of all renal veins of the subject, and by coupling anupstream end of the sleeve to a wall of the vena cava at a secondlocation that is upstream of all renal veins of the subject.

For some applications, the sleeve is configured to be coupled to thevena cava for less than one week, and the pump is configured to operatefor less than one week.

For some applications, the pump is configured to reduce blood pressurewithin the subject's renal veins by pumping blood.

For some applications, the pump is configured to pump blood from thecompartment to a site within the vena cava.

For some applications, the pump is configured to pump blood from thecompartment to a site of the vena cava that is upstream of the sleeve.

For some applications, the pump is configured to pump blood from thecompartment to a site of the vena cava that is downstream of the sleeve.

For some applications, the sleeve is shaped to define an opening throughwhich the pump is insertable.

For some applications, a diameter of the opening is between 2 mm and 10mm.

For some applications, the opening is sized such as to form a sealaround the pump.

For some applications, the apparatus further includes apump-accommodating sleeve protruding from the blood-impermeable sleeve,the pump accommodating sleeve being configured to accommodate insertionof the pump therethrough to the exterior of the blood impermeablesleeve.

For some applications, an inner diameter of the pump-accommodatingsleeve is between 2 mm and 10 mm.

For some applications, the pump-accommodating sleeve is sized such as toform a seal around the pump.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   placing a stent inside a blood vessel at a placement location of        the stent; and    -   at least partially anchoring the stent to the blood vessel at        the placement location by causing the blood vessel to constrict        around at least a portion of the stent, by applying a suctioning        force within the blood vessel.

For some applications, the blood vessel includes a blood vessel having agiven diameter at the placement location, and placing the stent insidethe blood vessel includes placing inside the blood vessel a stent havinga diameter that is less than the given diameter.

For some applications, causing the blood vessel to constrict around atleast the portion of the stent includes reducing an extent to which thestent is anchored to the blood vessel by virtue of oversizing of thestent, relative to if the blood vessel were not caused to constrictaround at least the portion of the stent.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a stent configured to be placed inside a blood vessel at a        placement location of the stent;    -   a pump configured to anchor the stent to the blood vessel at the        placement location by causing the blood vessel to constrict        around at least a portion of the stent, by applying a suctioning        force within the blood vessel.

For some applications, the blood vessel includes a blood vessel having agiven diameter at the placement location, and the stent includes a stenthaving a diameter that is less than the given diameter.

There is additionally provided, in accordance with some applications ofthe present invention, apparatus including:

-   -   a stent configured to be placed inside a blood vessel, the stent        being shaped to define widened ends thereof that are widened        relative to a central portion of the stent; and    -   a blood-impermeable sleeve coupled to the stent,        -   the sleeve defining flared ends thereof that are coupled to            the widened ends of the stent,        -   at least one of the flared ends of the sleeve being            configured to act as a valve by at least partially            separating from widened end of the stent to which it is            coupled in response to pressure being applied to the flared            end of the sleeve.

There is further provided, in accordance with some applications of thepresent invention, a method including:

-   -   placing into a blood vessel of a subject:        -   a stent shaped to define widened upstream and downstream            ends thereof that are widened relative to a central portion            of the stent, and        -   a blood-impermeable sleeve coupled to the stent, the sleeve            defining flared upstream and downstream ends thereof that            are coupled, respectively, to the widened upstream and            downstream ends of the stent; and    -   coupling the stent to the blood vessel such that:        -   in response to blood pressure on a first side of at least            one of the flared ends of the sleeve being greater than            blood pressure on a second side of the at least one flared            end of the sleeve, blood flows between an outside of the at            least one flared end of the sleeve and an inner wall of the            blood vessel, and        -   in response to blood pressure on the first side of the at            least one flared end of the sleeve being less than blood            pressure on the second side of the at least one flared end            of the sleeve, the at least one flared end of the sleeve            occludes blood flow between the outside of the at least one            flared end of the sleeve and the inner wall of the blood            vessel by contacting the inner wall of the blood vessel.

There is additionally provided, in accordance with some applications ofthe present invention, apparatus including:

-   -   a blood-impermeable sleeve defining flared ends thereof, and a        narrow central portion between the flared ends; and    -   a stent configured to be placed inside a blood vessel, the stent        being shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.

For some applications, the apparatus further includes a blood pump, theblood pump being configured to pump blood from between an outside of thesleeve and an inner wall of the blood vessel by being placed between theoutside of the sleeve and the vessel-wall-supporting frame.

For some applications, a diameter of the narrow central portion of thesleeve is between 8 mm and 35 mm.

For some applications, a maximum diameter of the flared ends of thesleeve is between 10 mm and 45 mm.

For some applications, a ratio of a maximum diameter of the flared endsof the sleeve, and a diameter of the narrow central portion of thesleeve is between 1.1:1 and 2:1.

For some applications, a maximum diameter of the vessel-wall-supportingframe is between 10 mm and 50 mm.

For some applications, a ratio of a maximum diameter of thewall-supporting frame to a diameter of the narrow central portion of thesleeve-supporting frame is between 1.1:1 and 5:1. For some applications,the ratio is greater than 1.5:1.

For some applications, a length of the sleeve is greater than 6 mm. Forsome applications, the length of the sleeve is less than 80 mm. For someapplications, a length of each one of the flared ends of the sleeve isgreater than 3 mm. For some applications, the length of each one of theflared ends of the sleeve is less than 40 mm. For some applications, alength of the narrow central portion of the sleeve is greater than 3 mm.For some applications, the length of the narrow central portion of thesleeve is less than 70 mm.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   placing into a blood vessel of a subject:        -   a blood-impermeable sleeve defining flared ends thereof, and            a narrow central portion between the flared ends, and        -   a stent shaped to define:            -   a sleeve-supporting frame that is shaped to define                widened ends thereof, and a narrow central portion                between the widened ends that is narrower than the                widened ends, the sleeve being coupled to the                sleeve-supporting frame of the stent; and            -   a vessel-wall-supporting frame coupled to the narrow                central portion of the sleeve-supporting frame and                radially protruding from the sleeve-supporting frame;                and    -   coupling the stent to the blood vessel such that the        vessel-wall-supporting frame of the stent holds open the blood        vessel by supporting the wall of the blood vessel, and the        sleeve-supporting frame supports the sleeve within the blood        vessel.

For some applications, the method further includes pumping blood from asite between an outside of the sleeve and an inner wall of the bloodvessel by placing a pump between the outside of the sleeve and thevessel-wall-supporting frame.

For some applications, placing the sleeve into the blood vessel includesplacing the sleeve into the blood vessel, a diameter of the narrowcentral portion of the sleeve being between 8 mm and 35 mm.

For some applications, placing the sleeve into the blood vessel includesplacing the sleeve into the blood vessel, a maximum diameter of theflared ends of the sleeve being between 10 mm and 45 mm.

For some applications, placing the sleeve into the blood vessel includesplacing the sleeve into the blood vessel, a ratio of a maximum diameterof the flared ends of the sleeve, and a diameter of the narrow centralportion of the sleeve being between 1.1:1 and 2:1.

For some applications, placing the stent into the blood vessel includesplacing the stent into the blood vessel, a maximum diameter of thevessel-wall-supporting frame being between 10 mm and 50 mm.

For some applications, placing the stent into the blood vessel includesplacing the stent into the blood vessel, a ratio of a maximum diameterof the wall-supporting frame to a diameter of the narrow central portionof the sleeve-supporting frame being between 1.1:1 and 5:1. For someapplications, placing the stent into the blood vessel includes placingthe stent into the blood vessel, the ratio being greater than 1.5:1.

For some applications, placing the sleeve into the blood vessel includesplacing the sleeve into the blood vessel, a length of the sleeve beinggreater than 6 mm. For some applications, placing the sleeve into theblood vessel includes placing the sleeve into the blood vessel, thelength of the sleeve being less than 80 mm. For some applications,placing the sleeve into the blood vessel includes placing the sleeveinto the blood vessel, a length of each one of the flared ends of thesleeve being greater than 3 mm. For some applications, placing thesleeve into the blood vessel includes placing the sleeve into the bloodvessel, the length of each one of the flared ends of the sleeve beingless than 40 mm. For some applications, placing the sleeve into theblood vessel includes placing the sleeve into the blood vessel, a lengthof the narrow central portion of the sleeve being greater than 3 mm. Forsome applications, placing the sleeve into the blood vessel includesplacing the sleeve into the blood vessel, the length of the narrowcentral portion of the sleeve being less than 70 mm.

There is further provided, in accordance with some applications of thepresent invention, a method for operating a blood pump disposed inside ablood vessel of a subject, the method including:

-   -   placing an occlusion element in the blood vessel, the occlusion        element having an occluding state thereof, in which the        occlusion element occludes the blood vessel, and a non-occluding        state thereof in which the occlusion element does not occlude        the blood vessel;    -   drawing blood in a downstream direction from a site that is in        fluid communication with an upstream side of the occlusion        element;    -   pumping blood into a site of the subject's vasculature that is        in fluid communication with a downstream side of the occlusion        element,    -   the pumping of the blood into the subject's vasculature being        performed in a manner that maintains the occlusion element in an        occluding state thereof, in which state the occlusion element        occludes the blood vessel.

For some applications, the method further includes performingultrafiltration on the blood prior to pumping the blood into the site ofthe subject's vasculature.

For some applications, placing the occlusion element in the blood vesselincludes placing the occlusion element in the blood vessel for less thanone week, and pumping the blood includes pumping the blood into thevasculature for less than one week. For some applications, placing theocclusion element in the blood vessel includes placing the occlusionelement in the blood vessel for more than one week, and pumping theblood includes pumping the blood into the vasculature for less than oneweek.

For some applications, the method further includes identifying thesubject as a subject suffering from a condition selected from the groupconsisting of: cardiac dysfunction, congestive heart failure, reducedrenal blood flow, increased renal vascular resistance, arterialhypertension, and kidney dysfunction, the blood vessel includes a renalvein of the subject, and drawing blood in the downstream direction fromthe site that is in fluid communication with the upstream side of theocclusion element includes, in response to identifying the subject assuffering from the condition, reducing blood pressure within thesubject's renal vein by drawing the blood in the downstream direction.

For some applications, pumping the blood into the subject's vasculaturein the manner that maintains the occlusion element in the occludingstate thereof includes pumping the blood into the subject's vasculaturesuch that hydrodynamic pressure of the blood that is pumped into thesubject's vasculature maintains the occlusion element in the occludingstate thereof.

For some applications, placing the occlusion element in the blood vesselincludes placing within the blood vessel a valve having valve leaflets,and pumping the blood into the subject's vasculature such thathydrodynamic pressure of the blood that is pumped into the subject'svasculature maintains the occlusion element in the occluding statethereof includes pumping the blood into the subject's vasculature suchthat the blood that is pumped into the subject's vasculature directlyimpacts downstream sides of the valve leaflets.

For some applications, placing the valve within the blood vesselincludes placing the valve within the blood vessel such that:

in response to blood pressure on an upstream side of the valve leafletsexceeding pressure on the downstream side of the valve leaflets, bloodflows in an antegrade direction between cusps of the valve leaflets andan inner wall of the blood vessel, and

in response to blood pressure on the downstream side of the valveleaflets exceeding pressure on the upstream side of the valve leaflets,the valve occludes retrograde blood flow by the cusps of the valveleaflets contacting the inner wall of the blood vessel.

For some applications, pumping the blood into the subject's vasculaturesuch that the blood that is pumped into the subject's vasculaturedirectly impacts downstream sides of the valve leaflets includesreducing blood clots at the valve leaflets, by flushing the valveleaflets.

For some applications, the method further includes pumping ananticoagulation agent into the subject's vasculature together with theblood that is pumped into the subject's vasculature, such that theanticoagulation agent directly impacts the valve leaflets.

For some applications, placing the valve in the blood vessel includesmaintaining portions of the valve leaflets in contact with a wall of theblood vessel by inflating a balloon.

For some applications, placing the valve in the blood vessel includesmaintaining portions of the valve leaflets in contact with a wall of theblood vessel by expanding portions of a slit tube radially outwardly.

For some applications, pumping the blood such that the blood directlyimpacts the downstream sides of the valve leaflets includes pumping theblood into the subject's vasculature via holes that are shaped to directthe blood toward the downstream sides of the valve leaflets.

For some applications, pumping the blood such that the blood directlyimpacts the downstream sides of the valve leaflets includes pumping theblood into the subject's vasculature via a pump catheter that is shapedto define a radial protrusion therefrom that is concavely curved towarda distal end of the catheter, the radial protrusion being configured todirect blood that is pumped into the vasculature toward the valveleaflets.

For some applications, pumping the blood such that the blood directlyimpacts the downstream sides of the valve leaflets includes pumping theblood into the subject's vasculature via holes that are disposedadjacent to bases of the valve leaflets.

For some applications, pumping the blood such that the blood directlyimpacts the downstream sides of the valve leaflets includes pumping theblood into the subject's vasculature via holes that are disposedadjacent to a location along lengths of the valve leaflets that is belowmidway between cusps of the leaflets and bases of the leaflets.

There is further provided, in accordance with some applications of thepresent invention, apparatus for use with a blood vessel of a subject,the apparatus including:

an occlusion element configured to be placed in the blood vessel, theocclusion element having an occluding state thereof, in which theocclusion element occludes the blood vessel, and a non-occluding statethereof in which the occlusion element does not occlude the bloodvessel;

-   -   a blood pump configured to:        -   draw blood in a downstream direction from a site that is in            fluid communication with an upstream side of the occlusion            element, and        -   pump blood into the subject's vasculature at a site that is            in fluid communication with a downstream side of the            occlusion element, the pump being configured to perform the            pumping of the blood into the blood vessel in a manner that            maintains the occlusion element in the occluding state            thereof.

For some applications, the blood pump is configured to performultrafiltration of the blood prior to pumping the blood into thesubject's vasculature.

For some applications, the occlusion element is configured to be placedin the blood vessel for less than one week, and the pump is configuredto pump blood into the vasculature for less than one week. For someapplications, the occlusion element is configured to be placed in theblood vessel for more than one week, and the pump is configured to pumpblood into the vasculature for less than one week.

For some applications, the pump is configured to perform the pumping ofthe blood into the subject's vasculature in the manner that maintainsthe occlusion element in the occluding state thereof, by pumping theblood into the subject's vasculature such that hydrodynamic pressure ofthe blood that is pumped into the subject's vasculature maintains theocclusion element in the occluding state thereof.

For some applications, the occlusion element includes a valve havingvalve leaflets, and the pump is configured to pump the blood into thesubject's vasculature such that the hydrodynamic pressure of the bloodmaintains the occlusion element in the occluding state thereof bypumping the blood into the subject's vasculature such that the bloodthat is pumped into the subject's vasculature directly impactsdownstream sides of the valve leaflets.

For some applications, the valve is configured such that:

-   -   in response to blood pressure on an upstream side of the valve        leaflets exceeding pressure on the downstream side of the valve        leaflets, blood flows in an antegrade direction between cusps of        the valve leaflets and an inner wall of the blood vessel, and    -   in response to blood pressure on the downstream side of the        valve leaflets exceeding pressure on the upstream side of the        valve leaflets, the valve closes by the cusps of the valve        leaflets contacting the inner wall of the blood vessel.

For some applications, the pump, by pumping the blood into the subject'svasculature such that the blood that is pumped into the subject'svasculature directly impacts downstream sides of the valve leaflets, isconfigured to reduce blood clots at the valve leaflets by flushing thevalve leaflets.

For some applications, the apparatus is for use with an anticoagulationagent, and the pump is configured to pump the anticoagulation agent intothe subject's vasculature together with the blood that is pumped intothe subject's vasculature, such that the anticoagulation agent directlyimpacts the valve leaflets.

For some applications, the apparatus further includes a balloonconfigured to maintain portions of the valve leaflets in contact with awall of the blood vessel by being inflated.

For some applications, the apparatus further includes a slit tubeconfigured to be inserted into the blood vessel and to maintain portionsof the valve leaflets in contact with a wall of the blood vessel byportions of the slit tube between the slits being expanded radiallyoutwardly.

For some applications, the blood pump is configured to be coupled to thevalve, the blood pump includes outlet holes via which the blood ispumped into the subject's vasculature, and the outlet holes are shapedsuch that when the blood pump is coupled to the valve, the outlet holesdirect the blood toward the downstream sides of the valve leaflets.

For some applications, the blood pump is configured to be coupled to thevalve, the blood pump includes a blood pump catheter that defines aradial protrusion therefrom that is concavely curved toward a distal endof the catheter, the radial protrusion being configured such that, whenthe blood pump is coupled to the valve, the radial protrusion directsblood that is pumped into the vasculature toward the valve leaflets.

For some applications, the blood pump is configured to be coupled to thevalve, the blood pump includes outlet holes via which the blood ispumped into the subject's vasculature, and the outlet holes are disposedon the blood pump such that, when the blood pump is coupled to thevalve, the holes are disposed adjacent to bases of the valve leaflets.

For some applications, the outlet holes are disposed on the blood pumpsuch that, when the blood pump is coupled to the valve, the outlet holesare disposed adjacent to a location along lengths of the valve leafletsthat is below midway between cusps of the leaflets and bases of theleaflets.

There is further provided, in accordance with some applications of thepresent invention, apparatus for use with a blood vessel of a subject,the apparatus including:

-   -   a blood pump configured to draw blood in a downstream direction        through the blood vessel into the pump; and    -   a valve including rigid portions thereof, the rigid portions        being configured to couple the valve to the blood vessel, the        valve being configured to be coupled to a distal portion of the        blood pump and to prevent blood from flowing past the valve in a        retrograde direction.

For some applications, the valve further includes flexible valveleaflets that are coupled to the rigid portions of the valve.

There is additionally provided, in accordance with some applications ofthe present invention, a method including:

-   -   providing a prosthetic valve that defines valve leaflets; and    -   placing the valve in a blood vessel such that:        -   in response to blood pressure on the upstream side of the            valve leaflets exceeding pressure on the downstream side of            the valve leaflets, blood flows in an antegrade direction            between cusps of the valve leaflets and an inner wall of the            blood vessel, and        -   in response to blood pressure on the downstream side of the            valve leaflets exceeding pressure on the upstream side of            the valve leaflets, the valve closes by the cusps of the            valve leaflets contacting the inner wall of the blood            vessel.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a prosthetic valve that includes flexible valve leaflets and a        rigid valve frame, the valve leaflets being coupled to the valve        frame such that:    -   in response to pressure on a first side of the valve leaflets        exceeding pressure on a second side of the valve leaflets, the        leaflets open by cusps of the valve leaflets separating from the        rigid frame, and    -   in response to blood pressure on the second side of the valve        leaflets exceeding pressure on the first side of the valve        leaflets, the valve closes by the cusps of the leaflets        contacting the rigid frame.

There is additionally provided, in accordance with some applications ofthe present invention, apparatus including:

-   -   a blood pump, including:        -   a tube;        -   first and second unidirectional valves disposed,            respectively, at proximal and distal ends of the tube;        -   a membrane coupled to the inside of the tube such as to            partition the tube into a first compartment that is in fluid            communication with the valves, and a second compartment that            is not in fluid communication with the valves; and        -   a pumping mechanism configured to pump fluid through the            tube by increasing and subsequently decreasing the size of            the first compartment by moving the membrane with respect to            the tube.

For some applications, the tube includes a stent, and material disposedon the stent.

For some applications, the occlusion element is configured to be placedin a blood vessel for less than one week.

For some applications, one of the valves is configured to preventbackflow of blood from the tube into the blood vessel and a second oneof the valves is configured to prevent backflow of blood from the bloodvessel into the tube.

For some applications, the blood pump is configured to be placed in arenal vein of a subject and to pump blood in a downstream direction fromthe renal vein to a vena cava of the subject.

For some applications, the blood pump is configured to occlude backflowof blood from the vena cava to the renal vein.

There is additionally provided, in accordance with some applications ofthe present invention, a method, including:

-   -   coupling a tube to an inner wall of a blood vessel of a subject,        -   first and second unidirectional valves being disposed,            respectively, at proximal and distal ends of the tube, and        -   a membrane being coupled to the inside of the tube, such as            to partition the tube into a first compartment that is in            fluid communication with the valves, and a second            compartment that is not in fluid communication with the            valves; and    -   operating a pumping mechanism to pump blood through the tube by        increasing and subsequently decreasing the size of the first        compartment, by moving the membrane with respect to the tube.

For some applications, the tube includes a stent and material disposedon a stent, and coupling the tube to the inner wall of the blood vesselincludes coupling the stent and the material to the inner wall of theblood vessel.

For some applications, coupling the tube to the inner wall of the bloodvessel includes coupling the tube to the inner wall of the blood vesselfor less than one week.

For some applications, operating the pumping mechanism includesoperating the pumping mechanism such that one of the valves preventsbackflow of blood from the tube into the blood vessel and a second oneof the valves prevents backflow of blood from the blood vessel into thetube.

For some applications, coupling the tube to the inner wall of the bloodvessel includes coupling the tube to an inner wall of a renal vein of asubject, and operating the pumping mechanism includes pumping blood in adownstream direction from the renal vein to a vena cava of the subject.

For some applications, coupling the tube to the inner wall of the renalvein includes occluding backflow of blood from the vena cava to therenal vein.

For some applications, the method further includes identifying thesubject as a subject suffering from a condition selected from the groupconsisting of: cardiac dysfunction, congestive heart failure, reducedrenal blood flow, increased renal vascular resistance, arterialhypertension, and kidney dysfunction, and operating the pump includes,in response to identifying the subject as suffering from the condition,reducing blood pressure within the subject's renal vein by operating thepump to pump blood in the downstream direction from the renal vein tothe vena cava.

There is further provided, in accordance with some applications of thepresent invention, a method including:

-   -   operating a blood pump to pump blood in a downstream direction        through a first vein, the first vein being a tributary of a        second vein and forming a junction with the second vein; and    -   preventing backflow of blood from the second vein to the first        vein by covering an ostium at the junction with an        ostium-covering umbrella disposed in the second vein.

For some applications, operating the blood pump includes performingultrafiltration on the pumped blood.

For some applications, the ostium-covering umbrella includes anostium-covering umbrella having a diameter of more than 6 mm when in anopen configuration, and covering the ostium with the umbrella includescovering the ostium with the umbrella having a diameter of more than 6mm.

For some applications, operating the blood pump includes causing theostium-covering umbrella to become sealed against a wall of the secondvein surrounding the ostium.

For some applications, the first vein includes a renal vein of thesubject, and the second vein includes a vena cava of the subject, andpumping blood in the downstream direction includes pumping blood in adownstream direction from the renal vein toward the vena cava.

For some applications, preventing backflow of blood from the second veinto the first vein includes preventing backflow of blood from the venacava to the renal vein.

For some applications, the method further includes identifying thesubject as a subject suffering from a condition selected from the groupconsisting of: cardiac dysfunction, congestive heart failure, reducedrenal blood flow, increased renal vascular resistance, arterialhypertension, and kidney dysfunction, and operating the pump includes,in response to identifying the subject as suffering from the condition,reducing blood pressure within the subject's renal vein by operating thepump to pump blood in the downstream direction from the renal vein tothe vena cava.

There is further provided, in accordance with some applications of thepresent invention, apparatus for use with a first vein of a subject, thefirst vein being a tributary of a second vein and forming a junctionwith the second vein, the apparatus including:

-   -   a catheter configured to be placed in the first vein, a distal        end of the catheter being configured to pump blood in a        downstream direction through the first vein and into the        catheter; and    -   an ostium-covering umbrella disposed around the outside of the        catheter and configured to be placed within the second vein at        the junction such that the umbrella prevents backflow of blood        from the second vein to the first vein by the ostium-occluding        umbrella covering an ostium at the junction from a location        within the second vein.

For some applications, the catheter, by pumping the blood is configuredto cause the ostium-covering umbrella to become sealed against a wall ofthe second vein surrounding the ostium.

For some applications, the ostium-covering umbrella has a diameter ofmore than 6 mm, when in an open configuration.

For some applications, the first vein includes a renal vein of thesubject, and the second vein includes a vena cava of the subject, andthe catheter is configured to pump blood by pumping blood in adownstream direction from the renal vein.

For some applications, the ostium-covering umbrella is configured toprevent backflow of blood from the vena cava to the renal vein by theostium-occluding umbrella covering an ostium at a junction of the renalvein and the vena cava, from a location within the vena cava.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

-   -   a catheter;    -   a pumping mechanism configured to suction fluid into a distal        end of the catheter; and    -   an ostium-covering umbrella disposed around the outside of the        catheter, the umbrella having a diameter of at least 6 mm when        in an open configuration thereof.

For some applications, the diameter of the ostium-covering umbrella isbetween 10 mm and 20 mm. For some applications, the diameter of theostium-covering umbrella is between 15 mm and 25 mm.

There is additionally provided, in accordance with some applications ofthe present invention, a method for measuring flow in a blood vesselincluding:

-   -   occluding the blood vessel with an occlusion element;    -   pumping blood from an upstream side of the occlusion element to        a downstream side of the occlusion element;    -   measuring blood pressure on the upstream and downstream sides of        the occlusion element;    -   modulating the pumping such that pressure on the downstream side        of the occlusion element is equal to pressure on the upstream        side of the occlusion element;    -   measuring a flow rate of blood through the pump when the        pressure on the downstream side of the occlusion element is        equal to pressure on the upstream side of the occlusion element;    -   designating the measured flow rate as a baseline flow rate; and    -   subsequently, measuring a flow rate of blood through the pump        relative to the baseline flow rate.

For some applications, the method further includes, in response todesignating the baseline flow rate, designating a baseline measure ofvascular resistance of the subject, and subsequently, measuring vascularresistance of the subject relative to the baseline vascular resistance.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B are schematic illustrations of a healthy subject's rightheart during diastole and systole respectively;

FIG. 1C is a set of graphs showing a healthy subject's central venousflow velocity profile and central venous pressure profile with respectto the subject's ECG cycle;

FIGS. 2A-B are schematic illustrations of the right heart of a subjectsuffering from congestive heart failure, during diastole and systolerespectively;

FIG. 2C is a set of graphs showing the central venous flow velocityprofile and central venous pressure profile of the subject sufferingfrom congestive heart failure, with respect to the subject's ECG cycle;

FIG. 3A is a schematic illustration of blood flowing back toward thekidneys of a subject suffering from congestive heart failure;

FIG. 3B is a set of graphs showing the central venous flow velocityprofile and renal vein pressure profile of the subject suffering fromcongestive heart failure, with respect to the subject's ECG cycle;

FIG. 4A is a schematic illustration of a pump and an occlusion elementplaced in left and right renal veins of a subject suffering fromcongestive heart failure, in accordance with some applications of thepresent invention;

FIG. 4B is a set of graphs showing the central venous flow velocityprofile and renal vein pressure profile of the subject suffering fromcongestive heart failure, with respect to the subject's ECG cycle,subsequent to placement of a blood pump in the subject's left and rightrenal veins, and activation of the blood pump, in accordance with someapplications of the present invention;

FIGS. 5A-D are schematic illustrations of an inverted valve disposedaround a blood pump catheter, in accordance with some applications ofthe present invention;

FIGS. 6A-G are schematic illustrations of configurations of the bloodpump catheter that are used with the inverted valve, in accordance withsome applications of the present invention;

FIGS. 7A-B are schematic illustrations of a blood pump catheter and anon-inverted valve placed in the renal vein, when the non-inverted valveis, respectively, in closed and open states thereof, in accordance withsome applications of the present invention;

FIGS. 8A-B are schematic illustrations of respective views of a bloodpump in accordance with some applications of the present invention;

FIGS. 9A-D are schematic illustrations of respective stages of a cycleof operation of the blood pump of FIGS. 8A-B, in accordance with someapplications of the present invention;

FIGS. 10A-D are schematic illustrations of a sleeve configured toocclude blood flow from a subject's vena cava to the subject's renalveins, in accordance with some applications of the present invention;

FIGS. 10E-F are schematic illustrations of a sleeve coupled to the venacava using a helical support element that is configured to occlude bloodflow from a subject's vena cava to the subject's renal veins, inaccordance with some applications of the present invention;

FIG. 10G is a schematic illustration a sleeve coupled to a helical bloodpump catheter, the sleeve and the blood pump catheter being configuredto occlude blood flow from a subject's vena cava to the subject's renalveins, in accordance with some applications of the present invention;

FIGS. 11A-C are schematic illustrations of a blood pump catheter beingplaced in a subject's renal vein, such that an ostium-covering umbrelladisposed around the outside of the catheter covers the ostium at thejunction between the subject's vena cava and the renal vein, inaccordance with some applications of the present invention;

FIGS. 12Ai-ii, and 12B-E are schematic illustrations of a blood pumpthat includes an impeller disposed inside a radially-expandable cage, inaccordance with some applications of the present invention;

FIGS. 13A-D are schematic illustrations of respective stages in a methodof manufacture of an impeller for a blood pump, in accordance with someapplications of the present invention;

FIGS. 14A-B are schematic illustrations of sutures tied around a portionof a frame of an impeller, in accordance with some applications of thepresent invention;

FIG. 15 is a schematic illustration of an impeller for a blood pump, inaccordance with some applications of the present invention;

FIGS. 16A-B are schematic illustrations of a three-bladed impeller for ablood pump, in accordance with some applications of the presentinvention;

FIG. 17 is a schematic illustration of a radially-expandable cage foruse with an impeller-based blood pump, in accordance with someapplications of the present invention

FIGS. 18Ai-18Aiii are schematic illustrations of respective views and/orconfigurations of a frame of an impeller, in accordance with someapplications of the present invention;

FIGS. 18Bi-18Biii are schematic illustrations of respective views and/orconfigurations of a frame of an impeller, the impeller frame of FIGS.18B1-18Biii being configured to define blades that span a largertransverse area than those of the impeller frame shown in FIGS.18Ai-18Aiii, in accordance with some applications of the presentinvention;

FIG. 18C is a schematic illustration of a radially-expandable cage thatincludes struts having undulated portions thereof, in accordance withsome applications of the present invention;

FIG. 18D is a schematic illustration of end views of radially expandedcages, in accordance with some applications of the present invention;

FIGS. 19A-B are schematic illustrations of an impeller cage that isshaped to define a generally cylindrical central portion in the absenceof any force being applied to the cage, in accordance with someapplications of the present invention;

FIG. 20 is a schematic illustration of an impeller cage that isconfigured to be placed inside a blood vessel, such as to cause thediameter of a portion of the blood vessel to be expanded relative to thediameter of the portion of the blood vessel in the absence of theimpeller cage, in accordance with some applications of the presentinvention;

FIG. 21A is a schematic illustration of impeller-based blood pumpsinserted into a subject's left and right renal veins via the subject'sfemoral vein, in accordance with some applications of the presentinvention;

FIG. 21B is a schematic illustration of impeller-based blood pumpsinserted into a subject's left and right renal veins via the subject'ssubclavian vein, in accordance with some applications of the presentinvention;

FIGS. 22Ai-ii, 22Bi-ii, and 22Ci-ii are schematic illustrations of athermal flow sensor and a housing that houses the thermal flow sensor,in accordance with some applications of the present invention; and

FIG. 23 shows graphs indicating the results of experiments that wereperformed on a pig, using an impeller-based blood pump, in accordancewith some applications of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIGS. 1A-B, which are schematic illustrationsof a healthy subject's heart during diastole and systole respectively.As shown in FIG. 1A, during diastole, blood flows from the subject'sright atrium (RA) 20 to the subject's right ventricle (RV) 22. As shownin FIG. 1B, during systole, the tricuspid valve 24, which separates theright ventricle from the right atrium, closes, as the right ventriclepumps blood toward the subject's lungs. During systolic long-axiscontraction of the right ventricle, the right atrium fills with bloodfrom the vena cava 26, the right atrium expanding such as to draw bloodinto the right atrium.

FIG. 1C is a set of graphs showing the central venous flow velocityprofile and central venous pressure profile of a healthy subject withrespect to the subject's ECG cycle. The flow velocity profile ischaracterized by biphasic forward flow, with flow during systole beinggreater than that during diastole. Typically, there is a small amount ofreverse flow AR, during atrial contraction. The central venous pressureprofile is characterized by relatively low pressure over the duration ofthe cardiac cycle, with the A-wave (i.e., the pressure during atrialcontraction), typically being greater than the V-wave (i.e., thepressure during systole).

Reference is now made to FIGS. 2A-B, which are schematic illustrationsof the heart of a subject suffering from congestive heart failure,during diastole and systole respectively. As shown in FIG. 2A, as withthe healthy heart, during diastole, blood flows from the subject's rightatrium 20 to the subject's right ventricle 22. As shown in FIG. 2B,during systole, due to right atrial pressure being too high, filling ofthe subject's right atrium is cut short, causing there to be an increasein pressure in the vena cava 26, as the high atrial pressure istransmitted to the vena cava. In some cases (e.g., in cases of very highright atrial pressure, tricuspid regurgitation, or atrial fibrillation),there may be retrograde flow of blood from the right atrium into thevena cava 26, and/or tributaries of the vena cava, due to the filling ofthe right atrium being cut short.

FIG. 2C is a set of graphs showing the central venous flow velocityprofile and central venous pressure profile of the subject sufferingfrom congestive heart failure, with respect to the subject's ECG cycle.The flow velocity profile is characterized by increased retrograde flowAR at the end of diastole, and by antegrade flow during systole beingless than that during diastole. For example, in some subjects there iszero flow, or reverse flow during systole. The central venous pressureprofile is characterized by relatively high pressure over the durationof the cardiac cycle with the V-wave being particularly high relative tothat of a healthy heart, and relative to the subject's A-wave.

Reference is now made to FIG. 3A, which is a schematic illustration ofblood flowing back toward the kidneys 30 of a subject suffering fromcongestive heart failure, via the subject's left and right renal veins32. FIG. 3B is a set of graphs showing the central venous flow velocityprofile and renal vein pressure profile of the subject suffering fromcongestive heart failure, with respect to the subject's ECG cycle. It isnoted that the graphs shown in FIG. 3B are the same as those shown inFIG. 2C, except that the pressure profile shown in FIG. 3B is that ofthe renal vein, whereas the pressure profile shown in FIG. 2C is thecentral venous pressure profile. As shown, typically, in the absence ofa device placed in the renal vein (as performed, in accordance with someapplications of the present invention), and assuming that the renal veinis at the same height as the central venous system, the renal venouspressure profile is identical to the central venous pressure profile.The renal vein pressure profile is characterized by relatively highpressure over the duration of the cardiac cycle, with the V-wave beingparticularly high relative to that of a healthy heart.

Reference is now made to FIG. 4A, which is a schematic illustration of ablood pump 34 and an occlusion element 36 placed in left and right renalveins 32 of a subject suffering from congestive heart failure, inaccordance with some applications of the present invention. The pump andthe occlusion element are typically placed inside the subject's renalveins in order to provide acute treatment of a subject suffering fromcardiac dysfunction, congestive heart failure, low renal blood flow,high renal vascular resistance, arterial hypertension, and/or kidneydysfunction. For example, the pump and the occlusion element may beplaced inside the subject's renal veins for a period of more than onehour (e.g., more than one day), less than one week (e.g., less than fourdays), and/or between one hour and one week (e.g., between one day andfour days). For some applications, the pump and the occlusion elementare chronically placed inside the subject's renal veins in order toprovide chronic treatment of a subject suffering from cardiacdysfunction, congestive heart failure, low renal blood flow, high renalvascular resistance, arterial hypertension, and/or kidney dysfunction.For some applications, a course of treatment is applied to a subjectover several weeks, several months, or several years, in which the pumpand the occlusion element are intermittently placed inside the subject'srenal veins, and the subject is intermittently treated in accordancewith the techniques described herein. For example, the subject may beintermittently treated at intervals of several days, several weeks, orseveral months.

The occlusion element is configured to occlude the renal vein at anocclusion site. The pump is configured to pump blood in a downstreamdirection, from a site that is in fluid communication with the upstreamside of the occlusion element to a site that is in fluid communicationwith a downstream side of the occlusion element. In doing so, the pumpreduces pressure in the renal vein. The occlusion element is configuredto protect the renal vein from backflow of blood from the vena cava tothe renal vein.

Typically, due to the reduction in pressure in the renal vein that iscaused by the pumping of the blood in the downstream direction,perfusion of the kidney increases. In turn, this may cause pressure inthe renal veins to rise relative to the pressure in the renal veinsimmediately subsequent to initiation of the pumping, due to increasedblood flow into the renal vein. Typically, even after perfusion of thekidney increases, the pump is configured to maintain the pressure in therenal vein at a lower value than the pressure in the renal vein beforethe initiation of the pumping. For some applications, in addition tolowering the subject's renal vein pressure, and/or increasing perfusionof the subject's kidney, the blood pump performs ultrafiltration on thesubject's blood.

It is noted that, for some applications, due to the reduction inpressure in the renal vein that is caused by the pumping of the blood inthe downstream direction, the subject's renal vascular resistancedecreases, in accordance with physiological mechanisms that aredescribed, for example, in an article by Haddy et al., entitled “Effectof elevation of intraluminal pressure on renal vascular resistance”(Circulation Research, 1956), which is incorporated herein by reference.It is further noted that a treatment of the subject that increases renalperfusion by increasing blood pressure in the subject's renal arterieswould typically not effect the aforementioned physiological mechanisms.

Typically, when blood pumps as described herein are used to reducepressure in the subject's renal veins, it is expected that there will bean improved responsiveness by the subject to administration of diureticsto the subject, due to the reduction in renal venous pressure.Therefore, for some applications, a reduced dosage of diuretics may beadministered to the subject relative to a dosage of diuretics that wouldbe administered to the subject in the absence of performing thetechniques described herein. Alternatively, a regular dosage ofdiuretics may be administered to the subject, but the diuretics may havea greater effect on the subject, due to the reduction in renal venouspressure.

High central venous pressure leads to a high level of blood pressurewithin the heart, which in turn leads to the release of atrialnatriuretic peptide (ANP) and B-type natriuretic peptide (BNP) by thesubject, both of which act as natural diuretics. Typically, when bloodpumps as described herein are used to reduce pressure in the subject'srenal veins, there is expected to be an improved responsiveness by thesubject to the release of the natural diuretics by the subject, due tothe reduction in renal venous pressure. For some applications, since thesubject's central venous pressure is not lowered by using the bloodpumps described herein, it is expected that the subject will continue torelease atrial natriuretic peptide (ANP) and B-type natriuretic peptide(BNP), even while the subject's renal venous pressure is reduced by theuse of the blood pumps described herein. Thus, for some applications,using the blood pumps described herein may result in the subjectcontinuing to release atrial natriuretic peptide (ANP) and B-typenatriuretic peptide (BNP), as well as resulting in the effectiveness ofthe aforementioned natural diuretics being greater than theeffectiveness of the diuretics in the absence of the use of the bloodpumps.

For some applications, pressure and/or flow sensors are disposed at thedistal end of the catheter, and the suction pressure that is applied tothe renal vein by the pump is modulated in response to feedback from thepressure and/or flow sensors. For example, a first pressure sensor 35may be disposed on the side of the occlusion element that is closer tothe kidney, and a second pressure sensor 37 may be disposed the side ofthe occlusion element that is closer to the vena cava. When the pumpingof the pump is initiated, the flow rate of the pumping is modulated(e.g., automatically modulated, or manually modulated), such as to causethe pressure measured by the first sensor (which is indicative of thepressure in the renal vein) to be equal to the pressure measured by thesecond sensor (which is indicative of the central venous pressure). Whenthe pressure measured at the first sensor is equal to that measured atthe second sensor, the pump control unit interprets the flow rate of thepumping to be indicative of the native blood flow rate from thesubject's renal vein to the subject's vena cava, since before theocclusion element were inserted into the renal vein, the renal veinpressure was equal to the central venous pressure. For someapplications, the pump control unit designates the aforementionedmeasured flow rate as a baseline flow rate. Subsequently, when the pumpis activated to lower the pressure in the renal vein relative thecentral venous pressure, the pump control unit measures the flow rate ofthe pumped blood relative the designated baseline flow rate.

For some applications, a third sensor (e.g., a non-invasive bloodpressure sensor, or an invasive blood pressure sensor) is used tomeasure the subject's arterial blood pressure. As described above, whenthe pumping of the pump is initiated, the flow rate of the pumping ismodulated, such as to cause the pressure measured by the first sensor tobe equal to the pressure measured by the second sensor. When thepressure measured at the first sensor is equal to that measured at thesecond sensor, the pump control unit determines a baseline measure ofthe subject's renal vascular resistance by measuring the differencebetween the measured arterial and venous pressures and dividing thedifference by the baseline flow rate. Subsequently, when the pump isactivated to lower the pressure in the renal vein relative the centralvenous pressure, the pump control unit measures the current renalvascular resistance (based upon the current difference between themeasured arterial and venous pressures and the current flow rate)relative the designated baseline renal vascular resistance.

FIG. 4B is a set of graphs showing the central venous flow velocityprofile and renal vein pressure profile of the subject suffering fromcongestive heart failure, with respect to the subject's ECG cycle,subsequent to placement of blood pump 34 and occlusion element 36 in thesubject's left and right renal veins 32. The renal venous pressure graphshows the original venous pressure profile as a dashed curve, and showstwo curves showing the renal venous pressure, subsequent to placement ofthe pumps and the occlusion elements in the veins, and activation of thepumps. Typically, subsequent to placement of the pumps and the occlusionelements in the veins and activation of the pumps, the height of thevenous pressure curve depends on the rate of pumping that the operatorapplies to the renal veins via the pumps. Therefore, two curves areshown for the renal venous pressure, subsequent to placement of thepumps and the occlusion elements in the veins, and activation of thepumps. As shown, placement of the pumps and the occlusion elements inthe veins, and activation of the pumps, typically causes a lowering andflattening of the renal vein pressure profile, even though the subject'scentral venous pressure is elevated. For some applications, the renalvein pressure profile is not completely flattened, since although thepump applies a constant suction pressure to the renal veins throughoutthe duration of the subject's cardiac cycle, small cyclical variationsin blood pressure are transmitted to the renal veins via the renalcapillary system. Alternatively, subsequent to placement of the pumpsand the occlusion elements in the veins, and activation of the pumps,the renal vein pressure profile is flattened.

Reference is now made to FIGS. 5A-D, which are schematic illustrationsof an inverted valve 40 disposed around a blood pump catheter 42, inaccordance with some applications of the present invention. Invertedvalve 40 is an example of occlusion element 36 described hereinabovewith reference to FIGS. 4A-B, and blood pump catheter 42 is an exampleof blood pump 34 described hereinabove with reference to FIGS. 4A-B.

Inverted valve 40 typically includes a rigid frame 44, which isconfigured to anchor the inverted valve to renal vein 32. (In FIGS.5A-B, inverted valve 40 is shown inside the left renal vein, but thescope of the present invention includes placing inverted valve 40 andblood pump catheter 42 in the right renal vein, and, as is typically thecase, placing inverted valve 40 and blood pump catheter 42 in each ofthe subject's renal veins.) Inverted valve 40 also includes valveleaflets 46. In response to blood pressure on the upstream side of thevalve leaflets exceeding pressure on the downstream side of the valveleaflets, the valve leaflets are configured to open by separating fromthe wall of the blood vessel (and typically by separating from the rigidframe of the valve), such that blood flows in an antegrade directionbetween cusps of the valve leaflets and an inner wall of the bloodvessel. In this sense, the inverted valve is inverted with respect toregular blood vessel valves, the leaflets of which are configured toopen by the cusps of the leaflets separating from one another in orderto allow blood flow between the leaflets, in response to blood pressureon the upstream side of the valve leaflets exceeding pressure on thedownstream side of the valve leaflets. Furthermore, a typical bloodvessel valve is disposed within the blood vessel such that the valveleaflets converge toward each other in the downstream direction,whereas, as shown in FIGS. 5A-B, leaflets 46 of valve 40 diverge fromeach other in the downstream direction.

FIG. 5A shows the inverted valve in an open state, arrows 48 indicatingblood flow in an antegrade direction between cusps of the valve leafletsand an inner wall of the renal vein 32. Typically, when inverted valve40 and blood pump catheter 42 are placed inside the renal vein, and theblood pump catheter is not activated, the valve leaflets will open, suchas to permit blood flow from the renal vein to the vena cava, inresponse to blood pressure within the renal vein exerting pressure onthe upstream side of leaflets 46.

FIG. 5B shows inverted valve 40 in the closed state. As shown, in theclosed state of the valve, the valve occludes blood flow from the renalvein to the vena cava, by the cusps of valve leaflets 46 contacting theinner wall of the renal vein at an occlusion site 49. For someapplications, in the occluding state of the valve, the cusps of thevalve leaflets contact a portion of the rigid frame of the valve.Typically, the valve closes in response to blood pressure on thedownstream side of the valve leaflets exceeding pressure on the upstreamside of the valve leaflets. When the catheter blood pump is activated,the pump draws blood in a downstream direction from a site that is influid communication with the upstream side of the valve, and pumps bloodback into the venous system at a site that is in fluid communicationwith a downstream side of the valve, such as a site within the vena cavaor a site within the renal vein. For example, the catheter blood pumpmay define inlet holes 50, which are in fluid communication with anupstream side of the valve, and through which blood is pumped into thepump, and the catheter blood pump may further define outlet holes 52,which are disposed in fluid communication with the downstream side ofthe valve, and through which blood is pumped into the renal vein or thevena cava. For some applications, the catheter blood pump pumps bloodusing an impeller 54 disposed inside a lumen 56 defined by the catheterblood pump, as shown.

For some applications, blood pump catheter 42 is coupled to frame 44 ofvalve 40 before blood pump catheter 42 and valve 40 are inserted intothe subject's body. The pump is coupled to the valve frame such that,upon being placed inside the renal vein, inlet holes 50 are in fluidcommunication with an upstream side of valve leaflets 46, and outletholes 52 are disposed in fluid communication with the downstream side ofthe valve. For some applications, valve 40 and blood pump catheter 42are inserted into the subject's renal vein separately. For example, thevalve may be inserted into the renal vein, and subsequently the bloodpump catheter may be inserted through the valve, such that the bloodpump catheter becomes coupled to valve frame 44. Alternatively the bloodpump catheter may be inserted into the renal vein, and subsequently, thevalve may be inserted into the renal vein over the blood pump catheter.Typically, the blood pump catheter and the valve frame define a couplingmechanism that couples the blood pump catheter to the valve frame suchthat inlet holes 50 are in fluid communication with an upstream side ofvalve leaflets 46, and such that outlet holes 52 are disposed in fluidcommunication with the downstream side of the valve.

Typically, blood pump catheter 42 is configured to pump blood into therenal vein in a manner that causes inverted valve 40 to assume anoccluding state thereof and/or a manner that maintains inverted valve 40in an occluding state thereof. For example, the blood pump catheter maybe configured to pump blood out of outlet holes 52 in such a manner thatblood flowing out of the outlet holes directly impacts the downstreamsides of valve leaflets 46, thereby causing the cusps of the leaflets toassume and/or maintain contact with the inner wall of the renal vein.Thus, hydrodynamic pressure of the blood that is pumped into thesubject's vasculature causes the cusps of the leaflets to assume and/ormaintain contact with the inner wall of the renal vein. For someapplications, blood pump catheter is structurally configured to pumpblood out of the outlet holes in the aforementioned manner, for example,in accordance with the applications of the present invention describedhereinbelow with reference to FIGS. 6B-D. Typically, valve 40 and bloodpump catheter 42 are configured such that, in response to blood pumpcatheter 42 becoming inactive (e.g., due to a loss of power to thepump), valve leaflets 46 will open to allow blood flow from the renalvein to the vena cava, in response to pressure being exerted on theupstream side of the valve leaflets by blood in the subject's renalvein.

As described above, for some applications, blood pump catheter 42 isconfigured to pump blood out of outlet holes 52 in such a manner thatblood flowing out of the outlet holes directly impacts the downstreamsides of valve leaflets 46. For some applications, pumping the blooddirectly against the downstream sides of the valve leaflets has anantithrombogenic effect, by the blood that is pumped against theleaflets flushing the leaflets, and reducing the build-up of blood clotsand/or tissue growth on the valve leaflets, relative to if the bloodwere not pumped directly against the valve leaflets. Alternatively oradditionally, the blood pump catheter pumps an anti-coagulation agentdirectly toward the leaflets together with the blood that is pumpeddirectly toward the leaflets. For some applications, by pumping ananti-coagulation agent directly toward the leaflets, a higher dose ofthe anticoagulation agent is provided to the leaflets than, for example,if the anticoagulation agent were to be systemically administered to thesubject. Thus, the dose of the anticoagulation agent that isadministered to the subject may be lowered relative to if theanticoagulation agent were to be systemically administered to thesubject, and/or the anticoagulation agent may be more effective atreducing blood clots and/or tissue growth at the leaflets relative to ifthe anticoagulation agent were to be systemically administered to thesubject. For some applications, the valve leaflets define small holestherethrough that are configured to permit the flow of theanticoagulation agent to the upstream sides of the valve leaflets.

In accordance with the description of FIGS. 5A-B, the combination ofinverted valve 40 and blood pump catheter 42 is thus configured suchthat (a) when the blood pump is inactive, the inverted valve opens, inresponse to pressure exerted on the upstream sides of the valve leafletsby blood in the renal vein, and (b) when the blood pump is active, thepumping of blood into the renal vein on the downstream side of leaflets46 maintains the valve in an occluding state thereof.

FIGS. 5C-D are schematic illustrations of views of the upstream ends ofinverted valve 40 and blood pump catheter 42, when the valve is,respectively, in a non-occluding, and an occluding state thereof. Asshown in FIG. 5C, when the valve is in the non-occluding state thereof,cusps 58 of leaflets 46 separate from the valve frame, such as to allowblood flow between the cusps of the valve leaflets and the inner wall ofthe blood vessel (blood vessel not shown). It is noted that, for someapplications, the structure of the valve frame is different from thatshown in FIGS. 5C-D. For example, the valve frame may have a structureas shown in FIGS. 5A-B, such that even when the valve is in theoccluding state thereof, the cusps of the leaflets are not in directcontact with a portion of the valve frame, but are in contact with theinner wall of the blood vessel.

Reference is now made to FIGS. 6A-G, which are schematic illustrationsof configurations of blood pump catheter that 42 are used with invertedvalve 40, in accordance with some applications of the present invention.

FIG. 6A shows pump control unit 60, which is used to control pumping ofblood pump catheter 42. The dashed boxes 62 indicate locations of theblood pump motor, in accordance with respective applications of theinvention. For some applications, the blood pump motor is disposed atthe location indicated by box 62A, outside of the subject's body, in thevicinity of the pump control unit (e.g., within the same housing as thepump control unit). For some applications, the motor being disposedoutside the subject's body allows the use of a smaller diameter catheterfor the blood pump catheter than would be required if the motor were tobe disposed inside the catheter. Alternatively, the blood pump motor isdisposed at the location indicated by box 62B, such that when the distalend of the blood pump catheter is disposed inside renal vein 32, themotor is disposed in the vena cava. For some applications, the motorbeing disposed in the portion of the catheter that is disposed in thevena cava, allows the distal portion of the catheter that is placedinside the renal vein to be smaller than would be required if the motorwere to be disposed inside the distal portion of the catheter. Furtheralternatively, the blood pump motor is disposed at the locationindicated by box 62C, within the distal portion of the catheter that isplaced inside the renal vein. For some applications, the blood pumpmotor is disposed in the vicinity of impeller 54 (e.g., at the locationindicated by box 62C) in order for the pump motor to more efficientlyimpart rotational motion to the impeller, relative to if the blood pumpmotor were disposed at a greater distance from impeller 54.

FIGS. 6B-D are schematic illustrations of blood pump catheter 42, thepump being structurally configured to pump blood out of outlet holes 52,in a manner that maintains inverted valve 40 in an occluding statethereof.

As shown in FIG. 6B, for some applications, the outlet holes are locatedsuch that when the blood pump catheter is placed through (e.g., coupledto) the valve and inlet holes 50 are disposed in fluid communicationwith the upstream side of the valve, the outlet holes are disposedadjacent to the bases 64 of valve leaflets 46. For example, the outletholes of the pump may be disposed adjacent to a location along thelength of the valve leaflets that is below midway between cusps 58 ofthe leaflets and bases 64 of the leaflets. Typically, due to thedisposition of the outlet holes with respect to the valve leaflets,blood flowing out of the outlet holes flows against the downstream sidesof valve leaflets 46, thereby causing the cusps of the leaflets tomaintain contact with the inner wall of the renal vein, i.e., therebymaintaining the valve in an occluding (i.e., closed) state.

For some applications, the blood pump catheter is shaped to define aradial protrusion 66 therefrom that is concavely curved toward a distalend of the catheter, as shown in FIG. 6C. The curvature and dispositionof protrusion 66 is typically such that a first end of the protrusion,which is coupled to the catheter, is disposed proximally to outlet holes52, and the other end of the radial protrusion is disposed distally tothe outlet holes. Typically, blood flowing out of the outlet holes isdirected toward the downstream sides of valve leaflets 46 by radialprotrusion 66, thereby causing the cusps of the leaflets to maintaincontact with the inner wall of the renal vein, i.e., thereby maintainingthe valve in an occluding (i.e., closed) state.

For some applications, outlet holes 52 are shaped such as to directblood out of the holes in a distal direction (i.e., toward the upstreamend of the catheter pump). For example, as shown in FIG. 6D, surfaces 68that define the holes may be curved toward the distal end of the pumpcatheter. Thus, the blood flowing out of the outlet holes is directedtoward downstream sides of valve leaflets 46, thereby causing the cuspsof the leaflets to maintain contact with the inner wall of the renalvein, i.e., thereby maintaining the valve in an occluding (i.e., closed)state.

FIGS. 6E-G show support structures that are used to support invertedvalve 40 within the renal vein as an alternative to, or in addition toframe 44 (shown in FIGS. 5A-D, for example).

For some applications, valve 40 is a tri-leaflet valve. Alternativelythe valve may be a bi-leaflet valve, or may have more than threeleaflets. The leaflets are maintained in contact with the renal vein atcommissures of the valve leaflets. Between the commissures of the valveleaflets, when the valve is in the occluding state of the valve, thecusps of the valve leaflets contact the renal vein wall, and when thevalve is in the non-occluding state of the valve, the cusps of the valveleaflets separate from the renal vein wall, such as to permit blood flowbetween the valve leaflets and the renal vein wall.

For some applications (shown in FIGS. 5A-D, for example), the leafletsare coupled to valve frame 44 at the commissures of the valve leaflets,and the valve frame maintains the commissures of the valve leaflets incontact with the renal vein wall. Alternatively or additionally, asshown in FIG. 6E, a slit tube 72 is advanced over blood pump catheter42. The tube is configured such that when the distal end of the tube ispushed toward the distal end of the catheter, the portions of the tubebetween the slits expand radially outwardly. The radially-expandedportions of the tube are configured to maintain commissures of the valveleaflets in contact with the renal vein wall.

Further alternatively or additionally, a balloon 74 having a star-shapedcross section (e.g., a three-pointed star cross section, as shown) isdisposed around the portion of the blood pump catheter 42 that isdisposed inside valve 40. Respective views of balloon 74, blood pumpcatheter 42, and valve 40 are shown in FIGS. 6F-G. For someapplications, the three-dimensional shape of balloon 74, when theballoon is in an inflated state thereof, is similar to the shape of acarambola (i.e., a star-fruit). Typically, the balloon is inflated suchthat at the points of the star of the balloon's cross-section, theballoon maintains the commissures of the valve leaflets in contact withthe renal vein wall.

As described hereinabove, typically, inverted valve 40 and blood pumpcatheter 42 are used to apply an acute treatment to a subject. Forexample, the inverted valve and the blood pump catheter may be placedinside the subject's renal veins for a period of more than one hour(e.g., more than one day), less than one week (e.g., less than fourdays), and/or between one hour and one week (e.g., between one day andfour days). For some applications, using the slit tube 72 or balloon 74to maintain the valve commissures in contact with the renal vein wallfacilitates removal of the valve from the renal vein, subsequent to thetermination of the treatment. For example, in order to remove the valvefrom the renal vein, the slit tube may be retracted such that theradially-expanded portions of the tube radially constrict, and the valveleaflets are no longer maintained in contact with the renal vein wall,and/or balloon 74 may be deflated such that the valve leaflets are nolonger maintained in contact with the renal vein wall.

Reference is now made to FIGS. 7A-B, which are schematic illustrationsof blood pump catheter 42 and a non-inverted valve 80, when thenon-inverted valve is, respectively, in occluding and non-occludingstates thereof, in accordance with some applications of the presentinvention. In some applications, as an alternative to being placedthrough an inverted valve, blood pump catheter 42 is inserted through anon-inverted valve, as shown in FIGS. 7A-B. Non-inverted valve 80 is anexample of occlusion element 36 described hereinabove with reference toFIGS. 4A-B. Non-inverted valve typically includes a rigid frame 82 andvalve leaflets 84.

Typically, blood pump catheter 42 is used to pump blood in a downstreamdirection from a site that is in fluid communication with an upstreamside of valve leaflets 84 to a site of the venous system that is influid communication with a downstream side of the valve leaflets, suchas a site within the vena cava or a site within the renal vein. Valve 80is configured to prevent backflow of blood by the cusps 86 of the valveleaflets contacting the catheter in response to pressure on thedownstream side of the valve leaflets exceeding pressure on the upstreamside of the valve leaflets. Valve 80 is further configured, in responseto pressure on the upstream side of the valve leaflets exceeding thepressure on the downstream side of the valve leaflets, to allow the flowof blood across the valve, by the cusps of the leaflets separating fromthe catheter, thereby allowing blood to flow between the leaflets andthe blood pump catheter in the direction of arrow 88 (FIG. 7A).

For some applications, initially, a combination of a valve (e.g., aninverted valve, as shown in FIGS. 5A-D, and 6A-G, or a non-invertedvalve, as shown in FIGS. 7A-B) and a pump is used to treat the subject.Subsequently (e.g., after a period of more than one hour, less than oneweek, and/or between one hour and one week), the pump is removed fromthe subject's renal vein, and the valve is left in place within therenal vein. Even in the absence of the pump, the valve is configured toreduce pressure in the subject's renal vein relative to renal pressurein the subject's renal vein in the absence of the valve, by preventingbackflow of blood from the subject's vena cava into the subject's renalvein and permitting the flow of blood from the subject's renal vein tothe subject's vena cava. Thus, for some applications, the valve is leftinside the renal vein in order to provide chronic treatment to thesubject, even after the acute treatment of the subject (using the pumpin combination with the valve) has terminated.

Reference is now made to FIGS. 8A-B, which are schematic illustrationsof respective views of a blood pump 90 in accordance with someapplications of the present invention. Pump 90 is an example of bothocclusion element 36 and pump 34 described hereinabove with reference toFIGS. 4A-B, since pump 90, when placed within the subject's renal vein,is configured to both occlude the renal vein and to pump blooddownstream from a site in fluid communication with an upstream side ofthe pump to a site that is in fluid communication with a downstream sideof the pump.

Pump 90 includes an outer tube 92, the outer surface of the tube beingconfigured to be in contact with the inner wall of the renal vein.Typically, outer tube 92 comprises a stent with material (typically, ablood-impermeable material) disposed thereon. First and secondunidirectional valves 94 and 96 are disposed at respective ends of thetube, the valves only permitting blood to flow into and out of the tubein the downstream direction. A membrane 98 is coupled to the inside ofthe tube, such that the membrane partitions the tube into a firstcompartment 100, which is in fluid communication with the valves, and asecond compartment 102, which is not in fluid communication with thevalves. A pumping mechanism 104, e.g., an electromagnetically-drivenpumping mechanism, cyclically drives the membrane to move with respectto the tube such that the relative sizes of the first and secondcompartments change.

Reference is now made to FIGS. 9A-D, which are schematic illustrationsof respective stages of a cycle of operation of blood pump 90, inaccordance with some applications of the present invention. FIG. 9Ashows the blood pump at an arbitrary starting point in the cycle ofoperation of the blood pump, at which point both valve 94 and valve 96are closed. As shown in the transition from FIG. 9A to FIG. 9B, and FIG.9B to FIG. 9C, pump mechanism 104 causes membrane 98 to move such thatthe volume of first compartment 100 increases, e.g., by the pumpingmechanism pumping fluid (e.g., air, or saline) out of the secondcompartment. The increase in the volume of the first compartment causesthe pressure inside the first compartment to decrease relative to thepressure on the upstream side of the first valve 94, causing valve 94 toopen and blood to be drawn into the first compartment. Subsequently, thepumping mechanism moves the membrane such as to increase the volume ofthe second compartment, e.g., by pumping fluid into the secondcompartment, as shown in the transition from FIG. 9C to FIG. 9D, andfrom FIG. 9D to FIG. 9A. The movement of the membrane causes the volumeof the first compartment to decrease, and pressure in the firstcompartment to increase. The pressure in the first compartment causesvalve 94 to close, and causes valve 96 to open and for blood that wasinside the first compartment to flow to the downstream side of pump 90.

Reference is now made to FIGS. 10A-D, which are schematic illustrationsof a blood-impermeable sleeve 110 configured to occlude blood flow froma subject's vena cava 26 to the subject's renal veins 32, in accordancewith some applications of the present invention. Typically, the sleeveis placed within the vena cava such that a downstream end 112 of thesleeve is coupled to the wall of the vena cava at a first location 114that is downstream of all renal veins of the subject (e.g., left andright renal vein in a typical subject that has two renal veins), andsuch that an upstream end 116 of the sleeve is coupled to a wall of thevena cava at a second location 118 that is upstream of all renal veinsof the subject. Thus, the sleeve isolates the blood in the renal veinsinto a compartment that is separated from blood flow through the venacava. Typically, a rigid structure, e.g., a stent 120 as shown, isconfigured to couple the upstream and downstream ends of the sleeve tothe vena cava.

A pump 122 is configured to pump blood from a location that is exteriorto sleeve 110 (i.e., from the isolated compartment) to a location thatis in fluid communication with the interior of the sleeve (e.g., alocation within the vena cava upstream or downstream of the sleeve).Thus, the pump pumps blood out of the subject's renal veins and into thesubject's vena cava. The sleeve prevents backflow of blood from the venacava into the renal veins.

For some applications, as shown, stent 120 defines flared ends thereof.Sleeve 110 also defines flared ends thereof. The flared ends of thesleeve are configured to occlude the flow of blood from the vena cava tothe renal veins by contacting the wall of the vena cava, if pressure inthe vena cava is greater than or equal to pressure in the renal veins.For some applications, at least one of the flared ends of the sleeve isconfigured to act as a valve, e.g., by providing blood flow from outsidethe sleeve to the vena cava in order to relieve pressure and/or anoverflow of blood outside the sleeve. In response to blood pressure inthe renal veins exceeding blood pressure in the vena cava, the flaredend of the sleeve is configured to at least partially separate from thewall of the vena cava, such that blood flows between the outside of theflared end of the sleeve and the inner wall of the vena cava. For someapplications, the upstream and the downstream ends of the sleeve areconfigured to act as a valve in the aforementioned manner, mutatismutandis. FIG. 10A shows the sleeve when the upstream and downstreamends of the sleeve are closed such as to occlude the flow of bloodbetween the outside of the sleeve and the wall of the vena cava. FIG.10B shows the sleeve, when the upstream and downstream ends of thesleeve are open, such as to allow the flow of blood from the renal veinsto the vena cava, between the outside of the sleeve and the wall of thevena cava.

As shown in FIGS. 10A-B and FIG. 10D, for some applications, apump-accommodating sleeve 124 protrudes from the outside of one of theflared ends of sleeve 110 (e.g., the downstream flared end of sleeve110, as shown). The pump-accommodating sleeve is shaped such as tofacilitate insertion of pump 122 therethrough. The pump-accommodatingsleeve is configured to form a seal around the pump, such that there isminimal or zero blood flow between the outside of the pump and theinside of the pump-accommodating sleeve. For some applications (notshown), rather than using pump-accommodating sleeve to form a sealaround the outside of the pump, the flared end of the sleeve defines anopening (e.g., a hole) through which the pump is inserted, the openingbeing sized such that the interface between the outside of the pump andflared distal end of the sleeve is sealed.

It is noted that, although pump-accommodating sleeve is shown protrudingfrom the outside of the flared upstream end of the sleeve, for someapplications the pump is inserted through the downstream flared end ofthe sleeve, and the downstream flared end of the sleeve defines apump-accommodating sleeve, or a hole through which the pump is inserted.In general, the scope of the present invention includes inserting theblood pumps and the occluding elements that are described herein towardthe renal veins by approaching the renal veins via the vena cava, fromabove the renal veins, or from below the renal veins. For example, therenal veins may be approached through the vena cava from the upstreamdirection, via the femoral vein, or from the downstream direction, viathe jugular vein.

In accordance with respective applications, pump 122 pumps blood intothe vena cava at a site that is upstream or downstream of the sleeve.For some applications, the pump pumps the blood into the vena cava at asite that is downstream of the sleeve such as to reduce the flow ofblood through the sleeve relative to if the pump were to pump the bloodinto the vena cava at a site that is upstream of the sleeve. For someapplications, it is advantageous to reduce the flow of blood through thesleeve in the aforementioned manner, since the sleeve acts as a resistorto blood flow through the sleeve. As described hereinabove, and as shownfor example in FIG. 10D, for some applications, the pump pumps bloodinto the vena cava at a site that is upstream of the sleeve.

For some applications, sleeve 110 and stent 120 are inserted into thesubject's vena cava, while a guidewire 126 is disposed insidepump-accommodating sleeve 124. Subsequent to anchoring sleeve 110 andstent 120 to the vena cava, pump 122 is inserted through thepump-accommodating sleeve, by advancing the pump over the guidewire.

As shown in FIG. 10C, for some applications stent 120 is shaped todefine a sleeve-supporting frame 128, which is generally shaped to matchthe shape of the sleeve. Typically, the sleeve-supporting frame isshaped to define widened ends 130 and a narrow central portion 132extending between the widened ends, the flared ends extending from theends of the of narrow central portion. In addition, the stent defines avessel-wall-supporting frame 134, which is coupled to narrow centralportion of the sleeve-supporting frame, and which protrudes radiallyoutwardly from the sides of the narrow central portion of thesleeve-supporting frame.

For some applications, pumping of blood by pump 122 from outside of thesleeve causes the walls of the vena cava to be pulled inwardly.Vessel-wall-supporting frame 134 supports the inner wall of the venacava, and prevents the inner wall of the vena cava from collapsingaround narrow central portion 132 of sleeve-supporting frame 128 of thestent. Typically, during operation of the pump, the pump head, includinginlet holes 125 of the pump head, is disposed in the gap between thenarrow central portion of the sleeve-supporting frame of the stent(which supports the sleeve) and the vessel-wall-supporting frame (whichsupports the wall of the vena cava).

As described hereinabove, for some applications, pumping of blood bypump 122 from outside of the sleeve causes the walls of the vena cava toconstrict by being pulled inwardly. For some applications, the pump isconfigured to anchor stent 120 to the vena cava by causing the vena cavato constrict around at least a portion of the stent, by applying asuctioning force to the vena cava. For some applications, a stent thatis not substantially oversized with respect to the vena cava, and/or astent having a diameter that is less than the diameter of the vena cavais anchored to the vena cava by virtue of the vena cava constrictingaround at least a portion of the stent, due to the suctioning forceapplied to the vena cava by the pump.

As described hereinabove, typically, sleeve-supporting frame 128 isshaped to generally match the shape of the sleeve. The sleeve and thesleeve-supporting frame define a narrow central portion diameter D1(FIG. 10C), and a maximum diameter D2 at the ends of the flared distalends of the sleeve. For some applications, D1 is greater than 8 mm, lessthan 35 mm, and/or between 8 and 35 mm. For some applications, D2 isgreater than 10 mm, less than 45 mm, and/or between 10 and 45 mm. Forsome applications, a ratio of D2:D1 is greater than 1.1:1, less than2:1, and/or between 1.1:1 and 2:1. For some applications, a total lengthL1 of the sleeve is greater than 6 mm, less than 80 mm, and/or between 6and 80 mm. For some applications, a length L2 of the flared ends of thesleeve (i.e., the length from the location at which the sleeve begins toflare, until the end of the sleeve) is greater than 3 mm, less than 40mm, and/or between 3 and 40 mm. For some applications, a length L3 ofthe narrow central portion of the sleeve and the sleeve-supporting frameis greater than 3 mm, less than 70 mm, and/or between 3 and 70 mm.

For some applications, a maximum diameter D3 of vessel-wall-supportingframe 134 of stent 120 is greater than 10 mm, less than 50 mm, and/orbetween 10 and 50 mm. For some applications, a ratio of D3:D1 is greaterthan 1.1:1 (e.g., greater than 1.5:1, or greater than 2:1), less than5:1, and/or between 1.1:1 and 5:1.

For some applications, an inner diameter D4 (FIG. 10A) ofpump-accommodating sleeve 124 is greater than 2 mm, less than 10 mm,and/or between 2 and 10 mm. For applications in which sleeve 110 definesan opening through which pump 122 is inserted, the diameter of theopening through which the pump is inserted is typically greater than 2mm, less than 10 mm, and/or between 2 and 10 mm.

For some applications, pump 122 is generally similar to blood pumpcatheter 42 described hereinabove, for example with reference to FIGS.5A-D. For example, as shown in FIG. 10D, the blood pump may include animpeller 123 to pump blood. Blood is drawn into the catheter from therenal veins via inlet holes 125, which are disposed between the outsideof the sleeve and the wall of the vena cava, and blood is pumped intothe vena cava via outlet holes 127 disposed in the vena cava, forexample at a location upstream of the sleeve, as shown in FIG. 10D.

Reference is now made to FIGS. 10E-F, which are schematic illustrationsof a blood-impermeable sleeve 135 coupled to vena cava 26 using ahelical support element 136 that is configured to occlude blood flowfrom the subject's vena cava to the subject's renal veins 32, inaccordance with some applications of the present invention. Inaccordance with respective applications the helical support element isan inflatable helical support element (e.g., a helical balloon), or ahelical support element that is made from a shape-memory alloy, such asnitinol. Typically, the helical support element becomes coupled to thevena cava such that a downstream end of the helical support element iscoupled to the wall of the vena cava at first location 114 that isdownstream of all renal veins of the subject (e.g., left and right renalvein in a typical subject that has two renal veins), and such that anupstream end of the helical support element is coupled to a wall of thevena cava at second location 118 that is upstream of all renal veins ofthe subject. Thus, the helical support element isolates the blood in therenal veins into a compartment outside the sleeve that is separated fromblood flow through the vena cava. It is noted that sleeve 135 does notnecessarily have flared ends that are configured to occlude blood flowfrom the vena cava to the renal veins by contacting wall of the venacava. Rather, as shown, the helical support element may occlude the flowof blood from the vena cava to the renal veins by contacting the wall ofthe vena cava. Alternatively, sleeve 135 has a generally similar shapeto sleeve 110 described hereinabove with reference to FIGS. 10A-D, thesleeve defining flared ends that are configured to contact the wall ofthe vena cava.

Typically, a blood pump catheter 137 is inserted into the vena cava viaa delivery device 138 (FIG. 10F). As shown in the transition from FIG.10E to FIG. 10F, for some applications, the blood pump catheter isguided into the compartment outside the sleeve by being advanced overthe helical support element. For some applications, a distal portion ofthe blood pump catheter is configured to assume a helical shapeautomatically upon being advanced out of the delivery device.Alternatively, by being advanced over the helical support element, thedistal portion of the blood pump catheter is made to assume a helicalshape. Typically, the blood pump catheter defines inlet holes 139 alongmost of the length (e.g., more than 50 percent, or more than 75 percentof the length) of the distal portion of the blood pump catheter (i.e.,the portion of the blood pump catheter that is placed inside thecompartment outside the sleeve by being advanced over the helicalsupport element). The blood pump catheter pumps blood out of thecompartment outside the sleeve (i.e., out of the renal veins) into theinlet holes. The blood pump typically defines outlet holes (not shown)that are configured to be disposed in the vena cava in fluidcommunication with the interior of the sleeve (e.g., at a location ofthe vena cava that is upstream of the sleeve, or a location of the venacava that is downstream of the sleeve). The pump pumps blood into thevena cava via the outlet holes.

Reference is now made to FIG. 10G, which is a schematic illustration ablood-impermeable sleeve 141 coupled to a helical blood pump catheter143, the sleeve and the blood pump catheter being configured to occludeblood flow from the subject's vena cava 26 to the subject's renal veins32, in accordance with some applications of the present invention.Typically sleeve 141 is shaped to define flared ends 145 thereof, asshown. Typically, sleeve 141 has a generally similar shape to sleeve 110described hereinabove with reference to FIGS. 10A-D, the sleeve definingflared ends that are configured to contact the wall of the vena cava.

Sleeve 141 and blood pump catheter 143 are inserted into the vena cavavia a delivery device 149. A distal end of the catheter 143 (i.e., theend of the catheter that is furthest from an insertion location viawhich the catheter is inserted into the subject's body) is coupled to adistal end of the sleeve (e.g., a downstream end of the sleeve, asshown) at a coupling location 147. The blood pump catheter is pre-shapedsuch that, upon being advanced out of the distal end of the insertiondevice, a distal portion of the catheter assumes a helical shape that isdisposed around the outside of the sleeve. Typically, by assuming thehelical shape, the distal portion of the catheter axially holds open thesleeve (i.e., prevents the sleeve from collapsing axially). For someapplications, a ring 151 made of a shape memory material (such asnitinol) is coupled to the proximal end of the sleeve and is configuredto support the proximal end of the sleeve. Typically, the blood pumpcatheter defines inlet holes 153 along most of the length (e.g., morethan 50 percent, or more than 75 percent of the length) of the distalportion of the blood pump catheter (i.e., the helical portion of theblood pump catheter that is disposed around the sleeve). The blood pumpcatheter pumps blood out from outside the sleeve (i.e., out of the renalveins) into the inlet holes. Typically the sleeve is placed in the venacava such that a downstream end of the sleeve is coupled to the wall ofthe vena cava at a first location 114 that is downstream of all renalveins of the subject (e.g., left and right renal vein in a typicalsubject that has two renal veins), and such that an upstream end of thesleeve is coupled to a wall of the vena cava at a second location 118that is upstream of all renal veins of the subject. Further typically,the pumping of the blood into the inlet holes causes the vena cava toconstrict around the outside of the sleeve such that blood in the renalveins becomes isolated into a compartment outside the sleeve that isseparated from blood flow through the vena cava.

The blood pump typically defines outlet holes (not shown) that areconfigured to be disposed in the vena cava in fluid communication withthe interior of the sleeve (e.g., at a location of the vena cava that isupstream of the sleeve, or a location of the vena cava that isdownstream of the sleeve). The pump pumps blood into the vena cava viathe outlet holes.

It is noted that although in FIGS. 10E-G the blood pump is shown beinginserted to outside the sleeve from the upstream end of the sleeve, forsome applications the pump is inserted to outside the sleeve from thedownstream end of the sleeve. In general, the scope of the presentinvention includes inserting the blood pumps and the occluding elementsthat are described herein toward the renal veins by approaching therenal veins via the vena cava, from above the renal veins, or from belowthe renal veins. For example, the renal veins may be approached throughthe vena cava from the upstream direction, via the femoral vein, or fromthe downstream direction, via the jugular vein.

Reference is now made to FIGS. 11A-C, which are schematic illustrationsof blood pump catheter 42 being placed in a subject's renal vein 32,such that an ostium-covering umbrella 140 disposed around the outside ofthe catheter, and disposed within the vena cava, covers an ostium at ajunction 142 between the subject's vena cava 25 and the renal vein 32,in accordance with some applications of the present invention. It isnoted that although the ostium-covering umbrella is described as an“umbrella,” the scope of the present invention includes covering theostium with any ostium-covering element that is configured to bedisposed around the outside of the catheter and that is made of flexibleportions (e.g., flexible tissue portions), and rigid support elementsthat provide shape and structure to the ostium-covering element.Ostium-covering umbrella 140 is an example of occlusion element 36described hereinabove with reference to FIGS. 4A-B, and blood pumpcatheter 42 is an example of blood pump 34 described hereinabove withreference to FIGS. 4A-B. (In FIGS. 11A-C, ostium-covering umbrella 140is shown covering the left renal vein ostium, but the scope of thepresent invention includes covering the right renal vein ostium withostium-covering umbrella 140, and, as is typically the case, placing anostium-covering umbrella at the ostia of the junctions of the vena cavawith each of the left and right renal veins.)

As shown in FIGS. 11A-C, blood pump catheter 42 and ostium-coveringumbrella 140 are inserted into vena cava 26 via an insertion device 144.During the insertion, the ostium-covering umbrella is typically in aclosed state thereof. The blood pump catheter and the ostium-coveringumbrella are advanced out of the insertion device, the ostium-coveringumbrella opening in response being advanced out of the distal end of theinsertion device (FIG. 11B). The ostium-covering umbrella is placed inthe vicinity of junction 142. Blood pump catheter is activated to pumpblood downstream through the renal vein into inlet holes 50 at thedistal end of the blood pump catheter. Typically, due to the suctionforce of the blood pump, the ostium-covering umbrella is pulled againstthe walls of the vena cava surrounding the ostium at junction 142 (FIG.11C).

Typically, ostium-covering umbrella 140 occludes backflow of blood fromthe vena cava to the renal vein, by being pushed against the walls ofthe vena cava surrounding the ostium at junction 142, in response toblood flowing from the vena cava to the renal vein. Further typically,while blood pump is active, ostium-covering umbrella occludes blood flowboth from the renal vein to the vena cava and from the vena cava to therenal vein, by the ostium-covering umbrella becoming sealed against thewalls of the vena cava surrounding the ostium at junction 142, due tothe suction force generated by the blood pump. In response to blood pumpcatheter 42 becoming inactive (e.g., due to a loss of power to thepump), surrounding the ostium at junction umbrella allows blood to flowfrom the renal vein to the vena cava in the direction of arrows 146(FIG. 11B), since when the pump is inactive the umbrella is not sealedagainst the walls of the vena cava surrounding the ostium at junction142.

For some applications, a diameter D5 of ostium-covering umbrella 140,when the ostium-covering umbrella is in an open state thereof is greaterthan 5 mm (e.g., greater than 10 mm, or greater than 20 mm), less than30 (e.g., less than 25 mm, or less than 20 mm), and/or between 5 and 30mm (e.g., between 10 and 20 mm, or between 15 and 25 mm).

Reference is now made to FIGS. 12Ai-ii and 12-B, which are schematicillustrations of a blood pump 150 that includes an impeller 152 disposedinside a radially-expandable impeller cage 154, in accordance with someapplications of the present invention. FIGS. 12Ai and 12Aii showrespective views of blood pump 150. Reference is further made to FIGS.12C-D, which show side views of blood pump 150 disposed inside renalvein 32, when cage 154 is, respectively, in relatively radially-expandedand radially-compressed configurations thereof, in accordance with someapplications of the present invention. Reference is also made to FIG.12E, which shows an end view of impeller 152 combined with across-sectional view of struts 204 of cage 154 and a cross-sectionalview of renal vein 32, when blood pump 150 is disposed inside renal vein32, in accordance with some applications of the present invention.

It is noted that the term “impeller” is used herein to denote a bladedrotor, as shown in FIGS. 12Ai-E. When the bladed rotor is placed insidea blood vessel (such as renal vein 32) and rotated, the bladed rotorfunctions as an impeller, by increasing the flow of blood through theblood vessel, and/or by generating a pressure difference between theupstream end and the downstream end of the impeller.

For some applications, blood pump 150 is placed one or both (or all) ofa subject's renal veins and is used to pump blood in a downstreamdirection through the renal veins toward the vena cava, such as toreduce renal vein pressure, and/or to enhance perfusion of the subject'skidneys.

Blood pump 150 is typically placed inside the subject's renal veins inorder to provide acute treatment of a subject suffering from cardiacdysfunction, congestive heart failure, low renal blood flow, high renalvascular resistance, arterial hypertension, and/or kidney dysfunction.For example, the pump may be placed inside the subject's renal veins fora period of more than one hour (e.g., more than one day), less than oneweek (e.g., less than four days), and/or between one hour and one week(e.g., between one day and four days). For some applications, the pumpis chronically placed inside the subject's renal veins in order toprovide chronic treatment of a subject suffering from cardiacdysfunction, congestive heart failure, low renal blood flow, high renalvascular resistance, arterial hypertension, and/or kidney dysfunction.For some applications, a course of treatment is applied to a subjectover several weeks, several months, or several years, in which the pumpis intermittently placed inside the subject's renal veins, and thesubject is intermittently treated in accordance with the techniquesdescribed herein. For example, the subject may be intermittently treatedat intervals of several days, several weeks, or several months.

Typically, the effect of pumping blood through the renal veins of asubject suffering from cardiac dysfunction, congestive heart failure,low renal blood flow, high renal vascular resistance, arterialhypertension, and/or kidney dysfunction is generally similar to thatdescribed with reference to FIG. 4B. Namely, the pumping causes alowering and flattening of the subject's renal vein pressure profile,even though the subject's central venous pressure is elevated. Inaccordance with the description of FIG. 4B hereinabove, the renal venouspressure graph shows the original venous pressure profile as a dashedcurve, and shows two curves showing the renal venous pressure,subsequent to activation of the blood pump. Typically, during pumping ofthe blood through the renal vein, the height of the venous pressurecurve depends on the amount of pumping that the operator applies to therenal vein via the pump, as indicated by the two solid curves shown inFIG. 4B, the curves representing renal venous pressure profiles atrespective rates of pumping of blood pump 150. For some applications, asshown, the renal vein pressure profile is not completely flattened,since small cyclical variations in blood pressure are transmitted to therenal veins via the renal capillary system.

Typically, due to the reduction in pressure in the renal vein that iscaused by the pumping of the blood in the downstream direction by pump150, perfusion of the kidney increases. In turn, this may cause pressurein the renal veins to rise relative to the pressure in the renal veinsimmediately subsequent to initiation of the pumping, due to increasedblood flow into the renal vein. Typically, even after perfusion of thekidney increases, the pump is configured to maintain the pressure in therenal vein at a lower value than the pressure in the renal vein beforethe initiation of the pumping. For some applications, in addition tolowering the subject's renal vein pressure, and/or increasing perfusionof the subject's kidney, the blood pump performs ultrafiltration on thesubject's blood.

It is noted that, for some applications, due to the reduction inpressure in the renal vein that is caused by the pumping of the blood inthe downstream direction by pump 150, the subject's renal vascularresistance decreases, in accordance with physiological mechanisms thatare described, for example, in an article by Haddy et al., entitled“Effect of elevation of intraluminal pressure on renal vascularresistance” (Circulation Research, 1956), which is incorporated hereinby reference. It is further noted that a treatment of the subject thatincreases renal perfusion by increasing blood pressure in the subject'srenal arteries would typically not effect the aforementionedphysiological mechanisms.

As described hereinabove, typically, when blood pump 150 is used toreduce pressure in the subject's renal veins, it is expected that therewill be an improved responsiveness by the subject to administration ofdiuretics to the subject, due to the reduction in renal venous pressure.Therefore, for some applications, a reduced dosage of diuretics may beadministered to the subject relative to a dosage of diuretics that wouldbe administered to the subject in the absence of performing thetechniques described herein. Alternatively, a regular dosage ofdiuretics may be administered to the subject, but the diuretics may havea greater effect on the subject, due to the reduction in renal venouspressure.

High central venous pressure leads to a high level of blood pressurewithin the heart, which in turn leads to the release of atrialnatriuretic peptide (ANP) and B-type natriuretic peptide (BNP) by thesubject, both of which act as natural diuretics. Typically, when bloodpump 150 is used to reduce pressure in the subject's renal veins, thereis expected to be an improved responsiveness by the subject to therelease of the natural diuretics by the subject, due to the reduction inrenal venous pressure. For some applications, since the subject'scentral venous pressure is not lowered by using blood pump 150, it isexpected that the subject will continue to release atrial natriureticpeptide (ANP) and B-type natriuretic peptide (BNP), even while thesubject's renal venous pressure is reduced by the use of the blood pump150. Thus, for some applications, using blood pump 150 may result in thesubject continuing to release atrial natriuretic peptide (ANP) andB-type natriuretic peptide (BNP), as well as resulting in theeffectiveness of the aforementioned natural diuretics being greater thanthe effectiveness of the diuretics in the absence of the use of bloodpump 150.

It is noted that, typically, blood pump 150 pumps blood in a manner thatenhances the rate of flow of blood flow through the renal veins and intothe vena cava, but does not cause a substantial change in the directionof the blood flow relative to the natural direction of flow through therenal veins, or from the renal veins to the vena cava (i.e., relative toblood flow in the absence of pumping by the pump). That is to say thatthe blood pump pumps blood in the downstream direction through the renalveins and then directly into the portion of the vena cava that isadjacent to the renal veins, rather than, for example, pumping the bloodfrom the renal veins into a different portion of the subject's veins(such as, an upstream location within the vena cava). Further typically,blood pump 150 enhances blood flow through the renal veins withoutremoving blood from the subject's venous system into a non-venousreceptacle, such as an artificial lumen of a blood pump.

Typically, cage 154 defines a non-constrained, radially-expandedconfiguration thereof, which the cage assumes in the absence of anyforce being applied to the cage, and a radially-compressedconfiguration, which the cage assumes when the cage is axiallyelongated. Similarly, typically, impeller 152 defines a non-constrained,radially-expanded configuration thereof, which the impeller assumes inthe absence of any force being applied to the impeller, and aradially-compressed configuration, which the impeller assumes when theimpeller is axially elongated.

Typically, during insertion of cage 154 and impeller 152 into thesubject's renal vein, the cage and the impeller are crimped by axiallyelongating the cage and the impeller, such that the cage and theimpeller become radially compressed. The cage and the impeller areinserted into the renal vein, while the cage and the impeller aremaintained in radially-compressed configurations by an insertion device155, e.g., a catheter. The cage and the impeller are advanced out of thedistal end of the insertion device into the renal vein. In response tobeing advanced out of the distal end of the insertion device, the cageand the impeller automatically radially expand, and axially contract.

Typically, cage 154 is configured to hold open the inner wall of therenal vein and to separate the inner wall of the renal vein from theimpeller, such that the renal vein does not become injured by theimpeller. Further typically, blood pump 150 includes an engagementmechanism 156 that is configured to engage the impeller with respect tothe cage. For example, as shown in FIG. 12B, which shows across-sectional view of the impeller and the cage, proximal and distalbearings 250P and 250D are disposed adjacent to the proximal and distalends of impeller 152, and are configured to impart rotational motion tothe impeller. Engagement mechanism 156 is disposed between a ring 202(described hereinbelow with reference to FIG. 17 ) disposed at thedistal end of the cage and a surface 252 of distal bearing 250P, suchthat when ring 202 moves distally, the ring pushes the engagementmechanism distally, which, in turn, pushes the distal bearing distally.The distal bearing is coupled to a distal ring 164 (describedhereinbelow with reference to FIGS. 13A-D) of the impeller, such thatthe distal motion of the distal bearing pulls the distal ring of theimpeller distally, thereby axially elongating the impeller.

The engagement mechanism thus engages the impeller with respect to thecage such that, in response to the cage becoming radially contracted andaxially elongated (e.g., in response to the renal vein exerting radialpressure on the cage), the impeller axially elongates and radiallycontracts. For example, as shown in the transition from FIG. 12C to FIG.12D, in response to the renal vein exerting pressure P on cage 154, thecage becomes partially radially compressed, causing the cage toelongate, e.g., by the distal end of the cage moving in the direction ofarrow 160. Engagement mechanism 156 causes the impeller to becomeelongated in response to the cage becoming elongated. The elongation ofthe impeller causes the impeller to radially contract.

Engagement mechanism 156 is typically configured such that, even at acircumferential location at which a separation Si (FIGS. 12C and 12D)between the impeller and the inner surface of the cage is smallest, aseparation between the impeller and the inner surface of the cage ismaintained (i.e., impeller and the inner surface of the cage are stillseparated from each other), even if the cage radially contracts. Afortiori, even at the circumferential location at which a separation S2between the impeller and the outer surface of the cage is smallest, theengagement mechanism maintains the separation between the impeller andthe outer surface of the cage (i.e., impeller and the outer surface ofthe cage are still separated from each other), even if the cage radiallycontracts. Since the inner wall of the renal vein is supported by theouter surface of the cage, separation S2 between the impeller and theouter surface of the cage is typically also the separation between theimpeller and the inner wall of the renal vein at the location at whichthe inner wall of the renal vein is closest to the impeller. Thus, theengagement mechanism maintains a separation between the between theimpeller and the inner wall of the renal vein, even at the location atwhich the inner wall of the renal vein is closest to the impeller, andeven when the renal vein exerts pressure on the cage such that the cageradially contracts.

It is noted that, in response to the renal vein exerting pressure P oncage 154 and causing the cage to radially contract, separation S1between the impeller and the inner surface of the cage, and/orseparation S2 between the impeller and the outer surface of the cage,may decrease. However, the engagement mechanism is such as to cause theimpeller and the inner surface of the cage to remain separated from eachother, even if the cage radially contracts. In this manner, the cageprotects the renal vein from being injured by the impeller even if therenal vein contracts. It is further noted that, although the inner wallof the renal vein is supported by the outer surface of the cage, thecage typically includes struts that defines cells, and the wall of therenal vein typically can protrude through the cells to inside the cage.By maintaining separation S1 between the impeller and the inner surfaceof the cage, the engagement mechanism protects the inner wall of therenal vein from the impeller even if the inner wall of the renal veinprotrudes to inside the cage.

When blood pump 150 is deployed inside a blood vessel, such as renalvein 32, cage 154 expands against the inner wall of the blood vessel,such that the cage becomes rotationally fixed with respect to the innerwall of the blood vessel. While the cage is rotationally fixed withrespect to the wall of the blood vessel, impeller 152 rotates such as topump blood through the blood vessel. Engagement mechanism 156 isconfigured to engage the impeller with respect to the cage such that (a)when the cage is radially compressed, the impeller becomes radiallycompressed, (b) when the cage is axially elongated, the impeller becomesaxially elongated, but (c) the impeller is able to rotate, even thoughthe cage is rotationally fixed in position. The engagement mechanism isconfigured to permit rotation of the impeller even though the cage isrotationally fixed in position, by the engagement mechanism permittingrotation of distal bearing 250D within the engagement mechanism.

Typically, in order to insert the cage and the impeller into the bloodvessel, the cage is placed inside insertion device 155 in a crimpedconfiguration. Typically, crimping the cage such that the cage assumesan axially-elongated configuration automatically causes the impeller toassume an axially-elongated configuration, since the engagementmechanism imparts the longitudinal motion of the distal end of the cageto the distal end of the impeller, in the manner described hereinabove.

As shown, for example, in FIG. 12C-D, for some applications, pressuresensors 157 and 159 are disposed on upstream and downstream sides ofblood pump 150. When blood pump 150 is disposed inside a renal vein, asshown in FIGS. 12C-D for example, the pressure measured by upstreampressure sensor 157 is indicative of blood pressure upstream of theblood pump in the renal vein, and the pressure measured by downstreampressure sensor 159 is indicative of central venous pressure. For someapplications, one or more further sensors 161 are disposed on the bloodpump (e.g., on a downstream side of the blood pump, as shown in FIG.12C-D, or on an upstream side of the blood pump), and are configured tomeasure one or more additional parameters, such as flow through therenal vein, and/or oxygen-saturation within the renal vein.Alternatively or additionally, a thermal flow sensor is used to measureflow through the renal vein. For example, a thermal flow sensor 260, asdescribed hereinbelow with reference to FIGS. 22Ai-Cii, may be used tomeasure flow through the subject's renal vein.

FIG. 12E shows an end view of impeller 152 combined with across-sectional view of struts 204 of cage 154 and a cross-sectionalview of renal vein 32, when blood pump 150 is disposed inside renal vein32, in accordance with some applications of the present invention. Thecross-sectional view of the cage and the renal vein is in a plane thatis perpendicular to a longitudinal axis 222 of the cage at alongitudinal location at the center of the longitudinal axis of thecage. Typically, at this location, the diameter of the cage,perpendicular to the longitudinal axis of the cage, is at its maximum.Further typically, at this location a span of the impeller SP,perpendicular to a longitudinal axis 224 of the impeller, is also at itsmaximum. For some applications, the outer edge of the impeller and theinner surfaces of struts of the cage are minimally separated from oneanother at this longitudinal location, and the outer edge of theimpeller and the outer surfaces of struts of the cage are minimallyseparated from one another at this longitudinal location.

Since the cage comprises struts 204, which are shaped to define cells,the cage typically allows blood flow therethrough, by allowing bloodflow through the cells defines by the cage. As shown in FIG. 12E,typically, when the cage and the impeller assume radially-expandedconfigurations thereof inside a blood vessel, such as renal vein 32,there is a minimum separation S1 between the outer edge of the impellerand struts 204, and a minimum separation S2 between the outer edge ofthe impeller and the outer surface of the struts 204 of the cage (whichis typically also the minimum separation between the outer edge of theimpeller and the inner wall of the blood vessel). Further typically,there is space between blades of the impeller. Typically, even if theimpeller is not actively pumping blood through the blood vessel, bloodis able to flow through the blood pump by flowing through the cellsdefined by the cage, and by flowing through the separations between theimpeller and the cage, through the separations between the impeller andthe blood vessel wall, and/or through the separation between the bladesof the impeller.

It is noted that blood pump 150 typically does not include an occlusionelement (such as a sealing element) for preventing retrograde flow ofblood through the blood pump. For some applications, while blood pump ispumping blood in an antegrade direction, there is some retrograde flowof blood through the separations between the impeller and the cage,through the separations between the impeller and the blood vessel wall,and/or through the separation between the blades of the impeller (e.g.,in the vicinity of the center of the impeller). Alternatively oradditionally, while blood pump is pumping blood in a downstreamdirection, there is antegrade flow of blood through the separationsbetween the impeller and the cage, through the separations between theimpeller and the blood vessel wall, and/or through the separationbetween the blades of the impeller (e.g., toward the center of theimpeller). Typically, whether the flow of blood through theaforementioned regions is in a retrograde or an antegrade direction, theflow of blood through these regions reduces a likelihood of bloodstagnating within these regions.

For some applications, when the impeller is in a non-constrained,radially-expanded configuration thereof (as shown in FIG. 12E), a spanSP of the impeller in a direction perpendicular to a longitudinal axisof the impeller is greater than 8 mm, less than 15 mm, and/or between 8and 15 mm. For example, span SP may be greater than 8 mm, less than 12mm, and/or between 8 mm and 12 mm. Or, span SP may be greater than 10mm, less than 15 mm, and/or between 10 mm and 15 mm.

Reference is now made to FIGS. 13A-D, which are schematic illustrationsof respective stages of a method of manufacture of impeller (i.e.,bladed rotor) 152, in accordance with some applications of the presentinvention. For some applications, a tube 162 (e.g., a nitinol, astainless steel, or a plastic tube) is cut (e.g., laser cut) along thedashed lines shown in FIG. 13A, such that the cut tube (FIG. 13B)defines a structure 165 having first and second end portions, e.g.,rings 164, at ends of the structures, the rings being connected to eachother by a plurality of (e.g., two as shown in FIG. 13B, or more thantwo) elongate elements 166 (e.g., elongate strips, as shown). The firstand second ends of each of the elongate elements are typically disposedat an angle alpha from one another with respect to the circumference ofthe rings. Typically, angle alpha is greater than 5 degrees (e.g.,greater than 50 degrees, greater than 70 degrees, or greater than 90degrees), less than 360 degrees (e.g., less than 180 degrees, less than150 degrees, or less than 110 degrees), and/or between 5 and 360 degrees(e.g., between 50 and 180 degrees, between 70 and 150 degrees, orbetween 90 and 110 degrees).

It is noted that, although elongate elements 166 are described and shownas strips, the scope of the present invention includes using elongateelements having other structures, such as elongate tubular structures,elongate rod structures, etc., mutatis mutandis.

Structure 165 is axially compressed, e.g., by pushing the two ringstoward one another, such that elongate elements 166 radially expand, asshown in the transition from FIG. 13B to FIG. 13C. Typically, before thestructure is axially compressed (i.e., in the axially elongatedconfiguration of the structure), a length L4 of the structure, measuredalong the longitudinal axis of the structure, is greater than 15 mm,less than 25 mm, and/or between 15 and 25 mm. Before the structure isaxially compressed (i.e., in the axially elongated configuration of thestructure), a length L5 of each of the elongate elements, measured alongthe longitudinal axis of the structure, is greater than 14 mm, less than22 mm, and/or between 14 and 22 mm. Typically, when impeller 152 isaxially elongated, the lengths of impeller 152 and of elongate elements166, measured along the longitudinal axis of the impeller, are the sameas, respectively, lengths L4 and L5. Further typically, when impeller152 is axially elongated, the lengths of impeller blades, measured alongthe longitudinal axis of the impeller, are the same as L5.

Typically, the structure is shape set in the axially-compressed state ofthe structure. Structure 165 forms the frame of the impeller 152.Further typically, in the axially-compressed state of the structure,each of elongate elements 166 of structure 165 forms a helical shape.Each of the helical elongate elements originates from a first one of theend portions (e.g., rings 164) and terminates at the second one of theend portions (e.g., rings 164). The pitches of each of the helicalelongate elements are typically within 20 percent of one another, thehelical elongate elements typically having the same pitch as oneanother. For some applications, the pitch of the helical elongateelements varies along the length of the helical elongate elements. Theradii of each of the helical elongate elements are typically within 20percent of one another, and, typically, the helical elongate elementshave the same radius as one another. For some applications, the helicesdefined by the two elongate elements are not symmetrical with respect toone another. The longitudinal axis of each one of the helical elongateelements is typically parallel to the longitudinal axis of the other oneof the helical elongate elements, and is typically parallel to thelongitudinal axis of the impeller. For some applications, each of theelongate elements defines more than one eighth of a winding of a helix,and/or less than half a winding of a helix, e.g., between one eighth ofa winding and half a winding of a helix.

It is noted that although each of the elongate elements is described asbeing helical, for some applications, the elongate elements do notdefine precise mathematical helices, but each of the elongate elementsdefines a generally helical shape in that the elongate element spiralsradially outwardly from a first one of end portions (e.g., rings) whileextending axially away from the first one of the end portions, and thenspirals radially inwardly toward the second one of the end portionswhile extending axially toward the second one of the end portions.

It is noted that, typically, cutting tube 162 such that angle alpha isas described hereinabove, facilitates the shaping of elongate elements166 into desired helical shapes. For some applications, the tube is cutsuch that angle alpha is not as described hereinabove, and neverthelesselongate elements 166 are shaped into desired helical shapes by twistingstructure 165, while applying a shape setting treatment to structure165. Typically, ceteris paribus, cutting tube 162 such that angle alphais as described hereinabove, facilitates the shaping of elongateelements 166 in desired helical shapes, while reducing stress onelongate elements 166, relative to stress on the elongate elements ifthe elongate elements are shaped into the desired helical shapes withoutcutting the tube such that angle alpha is as described hereinabove.

Typically, in the axially-compressed configuration of the structure, alength L6 of the structure, measured along the longitudinal axis of thestructure, is greater than 8 mm, less than 18 mm, and/or between 8 and18 mm. Further typically, in the axially-compressed configuration of thestructure, a length L7 of each of the elongate elements, measured alongthe longitudinal axis of the structure, is greater than 5 mm, less than14 mm, and/or between 5 and 14 mm. Typically, when impeller 152 is inits non-compressed, radially-expanded configuration, the lengths ofimpeller 152 and of elongate elements 166, measured along thelongitudinal axis of the impeller, are the same as, respectively,lengths L6 and L7. Further typically, when impeller 152 is in itsnon-constrained, radially-expanded configuration, the lengths ofimpeller blades, measured along the longitudinal axis of the impeller,are typically the same as L7.

Subsequent to axially compressing structure 165, a material 168 (e.g., aflexible polymeric material, such as silicone, polyurethane, and/orpolyester) is coupled to at least a portion of structure 165, e.g., tothe helical elongate elements of structure 165. Typically, material 168is coupled to the portion of structure 165 by structure 165 being dippedinto material 168, while material 168 is in a liquid state thereof. Forexample, structure 165 may be dipped into liquid silicone, asilicone-based elastomer, and/or a different elastomer. Subsequently,the material is dried (e.g., by a curing and/or a polymerizationprocess), such that a film of the material forms that is supported bythe helical elongate elements of structure 165. For some applications,techniques are used to facilitate the formation of a film on structure165 and/or coupling of the material to the helical elongate elements ofstructure 165, as described hereinbelow. For some applications, duringthe drying of material 168, structure 165 is rotated about itslongitudinal axis, such as to facilitate the formation of a film ofmaterial 168 having a uniform thickness. For some applications, material168 is coupled to structure 165 in a different manner to theabove-described manner, e.g., via suturing and/or electrospinning aflexible polymeric material (such as silicone, polyurethane, and/orpolyester) to the helical elongate elements of structure 165.

The helical elongate elements 166 with the material coupled theretodefine the impeller blade. To form impeller 152 with a single blade, asshown in FIG. 13D, tube 162 is cut to define a structure that definestwo helical elongate elements between rings 164. (It is noted that theimpeller shown in FIG. 13D may alternatively be described as atwo-bladed impeller, each of these elongate elements with the materialcoupled thereto defining a blade. For example, in the end view of theimpeller, shown in FIG. 18Ai, the portions of the impeller on respectivesides of ring 164 may each be viewed as blade. Nevertheless, in thecontext of the present application, an impeller that includes twohelical elongate elements, as shown in FIG. 13D, is described as havinga single blade.) For some applications, a three-bladed impeller isformed by cutting tube 162 to define a structure that defines threeelongate elements between rings 164, such that when the structure isaxially compressed the structure defines three helical elongateelements, e.g., as described hereinbelow with reference to FIGS. 16A-B.Alternatively or additionally, an impeller having a different number ofblades, e.g., 4-8 blades, is used.

Typically, material 168 is coupled to structure 165 such that thematerial forms a continuous layer (e.g., a continuous film) between theelongate elements 166. It is further noted that typically material 168is shaped to form one or more blades, by virtue of the material beingsupported by helical elongate elements 166 while the material is dried(e.g., by a curing or a polymerization process), and without requiringthe use of any instrument, such as a shaping mandrel, that is configuredto impart shape to the blades

As shown in FIG. 13D, the impeller blade is typically formed of acontinuous film of material 168 that is supported by helical elongateelements 166, the helical elongate elements typically forming the outeredges of the blade of the impeller. It is noted that, typically, theimpeller does not include an axial support member (such as a shaft)along the axis of the impeller between the proximal and distal ends ofthe helical elongate elements, for providing support to the film ofmaterial. More generally, the impeller typically does not include anysupport member (such as a shaft) between the proximal and distal ends ofthe helical elongate elements for providing support to the film ofmaterial 168. Thus, typically there is no supporting member that breaksup the continuity of the film of material disposed between the helicalelongate elements. Furthermore, rotational motion is imparted from theproximal end portion (e.g., proximal ring 164) of the impeller to thedistal end portion (e.g., distal ring 164) of the impeller via thehelical elongate elements of the impeller (e.g., substantially solelyvia the helical elongate elements), and not via an axial support member(such as a shaft).

During insertion of the impeller via insertion device 155 (FIG. 12Ai),the impeller is radially compressed by axially elongating structure 165,such that helical elongate elements 166 become straightened. Typically,the film of material 168 conforms with the shape changes that thehelical elongate elements undergo during the axial elongation ofstructure 165, since there is no additional supporting member providingsupport to material 168 between the proximal and distal ends of thehelical elongate elements. Further typically, ceteris paribus, the lackof an axial support member (such as a shaft) between the proximal anddistal ends of the helical elongate elements facilitates radialcompression of the impeller such that the maximum diameter of theimpeller when the impeller is in a maximally-radially-compressedconfiguration thereof is less than that of an impeller that is similarin all other aspects, but that includes an axial support member, i.e.,the impeller is configured to be radially compressible to a smallerdiameter than if the impeller were to comprise an additional supportingmember for supporting the material between the proximal and distal endsof the helical elongate elements.

For some applications, ceteris paribus, due to the lack of an axialsupport member (such as a shaft) between the proximal and distal ends ofthe helical elongate elements, the impeller is more flexible than animpeller that is similar in all other aspects, but that includes anaxial support member (such as a shaft). During the insertion into therenal vein, the impeller and the cage are typically inserted throughjunctions of blood vessels that form relatively acute angles with eachother (e.g., angles of more than 70 degrees), and that are disposed atrelatively short distances from one another. For example, the impellerand the cage may be passed through the femoral vein, the iliac vein,into the vena cava, and then into the renal vein. Flexibility of theimpeller typically facilitates insertion of the impeller into the renalvein.

Furthermore, ceteris paribus, the lack of an axial support member (suchas a shaft) between the proximal and distal ends of the helical elongateelements facilitates axial elongation of the impeller by a given lengthusing less force than would be required to axially elongate by the givenlength an impeller that includes an axial support member (such as ashaft) between the proximal and distal ends of the helical elongateelements, since axial elongation of an impeller that includes an axialsupport member would typically require axial elongation of the axialsupport member (e.g., via axial stretching of the support member).Similarly, ceteris paribus, if a given force is applied to the impellersuch as to cause the impeller to axially elongate, the axial elongationof the impeller is greater than the axial elongation that a generallysimilar impeller that includes an axial support member (such as a shaft)between the proximal and distal ends of the helical elongate elementswould undergo.

For some alternative applications of the present invention, material 168of the impeller itself is molded such as to facilitate the insertion ofan axial support member therethrough. For example, an elastomer (such assilicone or a silicone-based elastomer) may be used as material 168, andthe elastomer may be molded to form a hollow central lumen therethrough.An axial support member may be coupled to the impeller by being passedthrough the hollow central lumen defined by the elastomer.

Reference is now made to FIGS. 14A-B, which are schematic illustrationsof structure 165 from which impeller 152 is formed, the structure havingsutures 170 tied around a portion of the structure, in accordance withsome applications of the present invention. Reference is also made toFIG. 15 , which is a schematic illustration of an impeller 152, inaccordance with some applications of the present invention.

As described hereinabove, typically, material 168 is coupled to at leasta portion of structure 165 by structure 165 being dipped into material168, while material 168 is in a liquid state thereof. For example,structure 165 may be dipped into liquid silicone. Subsequently, thematerial is dried (e.g., by a curing and/or a polymerization process),such that a film of the material forms that is supported by the helicalelongate elements of structure 165. For some applications, in order tofacilitate the formation of a film of material 168 on structure 165,and/or in order to facilitate coupling of material 168 to helicalelongate elements 166, sutures 170 are tied around a portion ofstructure 165. For example, the sutures may be tied around helicalelongate elements 166 of structure 165, as shown in FIG. 14A, whichshows sutures 170 tied around helical elongate elements 166 beforematerial 168 has been coupled to structure 165.

For some applications, the sutures increase the surface area with whichmaterial 168 comes into contact, while material 168 is in its liquidstate. Alternatively or additionally, the surface of the sutures is morerough and/or porous than that of elongate elements 166 (which aretypically made of nitinol). Therefore, material 168 becomes coupled tothe sutures with a greater coupling strength than that of the couplingbetween material 168 and elongate elements 166. For some applications,the sutures act as mediators between a material from which the elongateelements are made, which typically has a relatively high stiffness (andis typically nitinol), and material 168, which is typically an elastomerhaving a relatively low stiffness. The sutures thereby enhance thestrength of the coupling between material 168 and helical elongateelements 166, when the material dries. For some applications, byenhancing the strength of the coupling between material 168 and helicalelongate elements 166, the sutures prevent gaps from forming between thematerial and helical elongate elements 166, during and/or after thedrying of material 168. In this manner, the sutures facilitate theformation of a continuous film of material 168 between the helicalelongate elements. FIG. 14B shows impeller 152, subsequent to theformation of a film of material 168 on structure 165, the film beingsupported by helical elongate elements 166 of structure 165.

Alternatively or additionally, in order to facilitate the formation of afilm of material 168 on structure 165, the edges of the end portions(e.g., rings 164) of structure 165 that are closest to helical elongateelements 166 define notches 180 therein, as shown in FIG. 15 . Asdescribed hereinabove, typically, material 168 is coupled to at least aportion of structure 165 by structure 165 being dipped into material168, while material 168 is in a liquid state thereof. For example,structure 165 may be dipped into liquid silicone. Typically, some of theliquid material enters into notches 180 in the end portions (e.g., rings164), such that the area of contact between the material and structureis increased relative to if the end portions did not define notches.Thus, the strength of the coupling of the material to structure 165 isstrengthened, when the material is subsequently dried.

Reference is now made to FIGS. 16A-B, which are schematic illustrationsof impeller 152, the impeller defining three blades 190, in accordancewith some applications of the present invention. Typically, impeller 152is manufactured to have three blades, using a generally similartechnique to that described hereinabove with reference to the impellerdescribed with reference to FIGS. 13A-D. However, rather than cuttingtube 162 (FIG. 13A) to define two elongate elements 166 (FIG. 13B), tube162 is cut define three elongate elements. The tube is then axiallycompressed, such that the elongate elements form three helical shapes,and the tube is shape set in the axially compressed configuration.Material 168 is then coupled to at least a portion of structure 165.Typically, the material is coupled to at least a portion of structure165 by structure 165 being dipped into material 168, while material 168is in a liquid state thereof. For example, structure 165 may be dippedinto liquid silicone. Typically the material is dried (e.g., by curing,and/or polymerization) onto the helical elongate elements such that thehelical elongate elements with the material coupled thereto forms athree-bladed impeller, as shown in FIG. 16A-B.

It is noted that, typically, the three-bladed impeller shown in FIGS.16A-B does not include an axial support member (such as a shaft) betweenthe proximal and distal ends of the helical elongate elements and alongthe axis of the impeller, for providing support to material 168. Moregenerally, typically, the impeller does not include a support member(such as a shaft) for providing support to material 168 in addition tothe helical elongate elements, between the proximal and distal ends ofthe helical elongate elements. Furthermore, rotational motion isimparted from the proximal end portion (e.g., proximal ring 164) of theimpeller to the distal end portion (e.g., distal ring 164) of theimpeller via the helical elongate elements of the impeller (e.g.,substantially solely via the helical elongate elements), and not via anaxial support member (such as a shaft).

During insertion of the impeller via insertion device 155 (FIG. 12Ai),the impeller is radially contracted by axially elongating the impeller,such that helical elongate elements 166 become straightened. Typically,material 168 conforms with the shape changes that the helical elongateelements undergo during the axial elongation of structure 165, sincethere is no additional supporting member (such as a shaft) providingsupport to material 168 between the proximal and distal ends of thehelical elongate elements. Further typically, ceteris paribus, the lackof an axial support member (such as a shaft) between the proximal anddistal ends of the helical elongate elements facilitates radialcompression of the impeller such that the maximum diameter of theimpeller when the impeller is in a maximally-radially-compressedconfiguration thereof is less than that of an impeller that is similarin all other aspects, but that includes an axial support member, i.e.,the impeller is configured to be radially compressible to a smallerdiameter than if the impeller were to comprise an additional supportingmember for supporting the material between the proximal and distal endsof the helical elongate elements.

For some applications, ceteris paribus, due to the lack of an axialsupport member (such as a shaft) between the proximal and distal ends ofthe helical elongate elements the impeller is more flexible than animpeller that is similar in all other aspects, but that includes anaxial support member (such as a shaft). During the insertion into therenal vein, the impeller and the cage are typically inserted throughjunctions of blood vessels that form relatively acute angles with eachother (e.g., angles of more than 70 degrees), and that are disposed atrelatively short distances from one another. For example, the impellerand the cage may be inserted into the renal vein by being passed throughthe femoral vein, the iliac vein, into the vena cava, and then into therenal vein. Flexibility of the impeller typically facilitates insertionof the impeller into the renal vein.

Furthermore, as described hereinabove, the lack of an axial supportmember (such as a shaft) between the proximal and distal ends of thehelical elongate elements facilitates axial elongation of the impellerby a given length using less force than would be required to axiallyelongate by the given length an impeller that includes an axial supportmember (such as a shaft) between the proximal and distal ends of thehelical elongate elements. Similarly, ceteris paribus, if a given forceis applied to the impeller such as to cause the impeller to axiallyelongate, the axial elongation of the impeller is greater than the axialelongation that a generally similar impeller that includes an axialsupport member (such as a shaft) between the proximal and distal ends ofthe helical elongate elements would undergo.

For some alternative applications of the present invention, material 168of the impeller itself is molded such as to facilitate the insertion ofan axial support member therethrough. For example, an elastomer (such assilicone or a silicone-based elastomer) may be used as material 168, andthe elastomer may be molded to form a hollow central lumen therethrough.An axial support member may be coupled to the impeller by being passedthrough the hollow central lumen defined by the elastomer.

Reference is now made to FIG. 17 , which is a schematic illustration ofprotective cage 154 of blood pump 150, in accordance with someapplications of the present invention. Typically, the cage comprisesproximal and distal rings 202. Between the proximal and distal rings,the cage comprises struts 204, which are shaped to define cells. Forsome applications, in a non-compressed, radially-expanded configurationof the cage (i.e., in the absence of any force being applied to thecage), between the proximal and distal rings, the cage defines agenerally spherical or ovoid shape, as shown in FIG. 17 . Engagementmechanism 156 (FIG. 12B) typically engages the impeller with respect tocage 154 via rings 164 (FIGS. 13A-D) of the impeller, rings 202 of thecage, and distal bearing 250D (FIG. 12B).

For some applications, when cage 154 is in its radially-expandedconfiguration, a length L8 of the cage, measured along the longitudinalaxis of the cage, and including rings 202 of the cage, is greater than17 mm, less than 26 mm, and/or between 17 and 26 mm. A length L9 of thecage, measured along the longitudinal axis of the cage, and notincluding rings 202 of the cage, is greater than 12 mm, less than 21 mm,and/or between 12 and 21 mm. For some applications, when the cage isaxially elongated, and radially compressed, by being crimped(configuration not shown), the length of the cage, measured along thelongitudinal axis of the cage, and including rings 202 of the cage, isgreater than 22 mm, less than 35 mm, and/or between 22 and 35 mm.Typically, for such applications, when the cage is axially elongated bybeing crimped (configuration not shown), the length of the cage,measured along the longitudinal axis of the cage, and excluding rings202 of the cage is greater than 18 mm, less than 30 mm, and/or between18 and 30 mm. For some applications, when cage 154 is in itsradially-expanded configuration, a diameter D7 of the cage is greaterthan 8 mm, less than 20 mm, and/or between 8 and 20 mm. For example,diameter D7 may be greater than 8 mm, less than 15 mm, and/or between 8mm and 15 mm. Or, diameter D7 may be greater than 13 mm, less than 19mm, and/or between 13 mm and 19 mm.

The cage is typically inserted into a blood vessel (e.g., into the renalvein), while in a crimped configuration thereof (i.e., while the cage isaxially elongated and radially compressed with respect to thenon-compressed configuration of the cage). As described hereinabove,during insertion of the impeller into the blood vessel, the impeller isradially contracted by axially elongating structure 165, such thathelical elongate elements 166 become straightened. Typically, the filmof material 168 conforms with the shape changes that the helicalelongate elements undergo during the elongation of the impeller. Furthertypically, during insertion of the blood pump into the blood vessel,impeller 152 is already disposed inside the cage. Thus, during insertionof blood pump 150 into the blood vessel, impeller 152 is disposed insidethe cage, while the cage is in a crimped configuration thereof, andwhile the impeller is in an axially-elongated configuration thereof, inwhich the helical elongate elements of the impeller are straightened.Typically, in response to being released from the insertion deviceinside the blood vessel, the cage automatically assumes thenon-compressed, radially-expanded configuration of the cage. Similarly,the impeller typically automatically radially expands inside the cagesuch as to assume a non-compressed, radially-expanded configurationthereof, in response to the cage and the impeller being released fromthe insertion device.

Reference is now made to FIGS. 18Ai-18Aiii, which are schematicillustrations of examples of structure 165 which forms the frame ofimpeller 152, in accordance with some applications of the presentinvention.

As indicated by inner dashed circle 194, which is the same size in bothFIG. 18Ai-18Aiii, the impellers shown in each of FIGS. 18Ai and 18Birotate such as to encompass a circular area having the same size. Thus,as indicated by outer dashed circle 196, which is the same size in bothFIG. 18Ai-18Aiii, the impellers shown in each of FIGS. 18Ai and 18Bi aresuitable for being placed inside a blood vessel having a given crosssectional area, such that there a separation between the inner wall ofthe blood vessel and the impeller, as described hereinabove. (The outerdashed circle is representative of the cross-section of the inner wallof blood vessel into which the impeller is placed.) Despite beingsuitable for being placed in similarly sized blood vessels, structure165 of the impeller shown in FIGS. 18Bi-18Biii is configured such thatthe blades of the impeller formed from the structure span a largertransverse area than the impeller blades formed by structure 165 asshown in FIGS. 18Ai-18Aiii. In other words, when viewed from an end ofthe impeller (as shown in FIGS. 18Ai and 18Bi), then the blades of theimpeller frame shown in FIGS. 18Bi-18Biii span a transverse area (i.e.,an area transverse to the axis of the impeller), that is greater thanthe transverse area that is spanned by the blades of the impeller frameshown in FIGS. 18Ai-18Aiii. Similarly, when viewed from an end of theimpeller (as shown in FIGS. 18Ai and 18Bi), then each of the blades ofthe impeller frame shown in FIGS. 18Bi-18Biii defines an angle thetaabout the longitudinal axis of the impeller that is less than thatdefined by each of the blades of the impeller frame shown in FIGS.18Ai-18Aiii.

Typically, ceteris paribus, for an impeller that is placed inside ablood vessel having a given diameter, the propulsion of blood throughthe blood vessel at a given rotation rate of the impeller is greater(and, therefore, the efficiency of the impeller is greater), the greaterthe transverse area of the blood vessel (i.e., the area of the bloodtransverse to the longitudinal axis of the blood vessel) that the bladesof the impeller span. For an impeller as shown in FIGS. 18Ai-iii and18Bi-iii, the efficiency of the impeller is typically greater, thegreater the angle theta defined by the impeller blade about each side ofthe longitudinal axis of the impeller. Thus, with reference to FIGS.18Ai-18Aiii and 18Bi-18Biii, ceteris paribus, the impeller shown inFIGS. 18Bi-18Biii would typically pump blood more efficiently than thatshown in FIGS. 18Ai-18Aiii. However, as is explained in greater detailhereinbelow, when the impellers are axially elongated, then, ceterisparibus, an impeller that defines blades spanning a larger transversearea, will typically be longer than an impeller that defines bladesspanning a smaller transverse area.

It is noted that, for some applications, a single-bladed impeller asdescribed herein is used, and the value of theta (i.e., the angledefined by the blade of the impeller about each side of the longitudinalaxis of the impeller) is greater than 5 degrees (e.g., greater than 50degrees, greater than 70 degrees, or greater than 90 degrees), less than360 degrees (e.g., less than 180 degrees, less than 150 degrees, or lessthan 110 degrees), and/or between 5 and 360 degrees (e.g., between 50and 180 degrees, between 70 and 150 degrees, or between 90 and 110degrees).

During insertion of blood pump 150 into the blood vessel, impeller 152is typically disposed inside cage 154, while the cage is in anaxially-elongated, crimped configuration thereof, and while the impelleris in an axially-elongated, crimped configuration thereof. Therefore,the length that the impeller defines when the impeller is in itsaxially-elongated, crimped configuration is typically less than thelength of the cage when the cage is in its axially-elongated, crimpedconfiguration. In turn, the dimensions of the cage are limited, sincethe diameter of the cage in the radially-expanded configuration of thecage is limited based upon the size of the blood vessel into which theblood pump is to be placed.

For some applications, the cage is configured to include struts 204 thatare shape set such as to include undulating portions 210, as shown inFIG. 18C (which is described in further detail hereinbelow). Typically,the level of undulation of the undulated portions of the struts of thecage when the cage is in its radially-expanded configuration, is greaterthan the level of undulation of the undulated portions of the strutswhen the cage is in its axially elongated configuration. For someapplications, by including struts that have undulating portions, a cagethat has a given diameter and/or outer profile in its radially-expandedconfiguration can be elongated to define a greater length when the cageis elongated than a cage having a similar diameter and/or outer profilethat does not include struts that have undulating portions. In thismanner, the cage (a) is able to accommodate an impeller which in itsaxially-elongated configuration is longer (and which, in itsradially-expanded configuration, therefore defines a larger transversearea), than a cage that did not include struts that have undulatingportions would be able to accommodate, but (b) the diameter and/or outerprofile of the cage in its radially-expanded configuration is generallysimilar to the cage that does not include struts that have theundulating portions.

There follows a more detailed description of FIGS. 18Ai-18C.

As described hereinabove, structure 165 of the impeller shown in FIGS.18Bi-18Biii is configured such that the blades of the impeller formedfrom the structure span a larger transverse area than the impellerblades formed by structure 165 as shown in FIGS. 18Ai-18Aiii. FIGS.18Aii and 18Bii show side views of the two examples of structure 165,and FIGS. 18Aiii and 18Biii show views of the examples of structure 165in the axially-elongated configurations of the structures, in which thehelical elongate elements of the structures are straightened. Asdescribed hereinabove, during insertion of blood pump 150 into the bloodvessel, the impeller is typically in the axially-elongatedconfiguration, as shown in FIGS. 18Aiii and 18Biii. In order for theimpeller blades to span a larger transverse area (as shown in FIG.18Bi), the lengths of elongate elements 166 typically are longer thanthose of an impeller having blades that span a smaller transverse area(as shown in FIG. 18Ai). Therefore, when the impellers are in theaxially-elongated configurations thereof, length LB of impeller shown inFIGS. 18Bi-18Biii is greater than length LA of the impeller shown inFIGS. 18Ai-18Aiii.

Reference is now made to FIG. 18C, which is a schematic illustration ofcage 154 the cage including at least some struts 204 that have undulatedportions 210 thereof, in accordance with some applications of thepresent invention. Reference is also made to FIG. 18D, which is aschematic illustration of end views of radially expanded cages 154, oneof which includes struts 204 having undulated portions 210 thereof (theleft cage), and the other one of which does not include struts havingundulated portions thereof (the middle cage), in accordance with someapplications of the present invention. On the right of FIG. 18D, thecage that includes struts having undulated portions thereof is overlaidon the cage that does not include struts having undulated portionsthereof, with the struts that include undulated portions shown withsolid lines, and the corresponding struts of the second cage that do notinclude undulated portions being shown with dashed lines. As may beobserved in the portion of the FIG. 18D that shows the overlaid cages,the inclusion of undulated portions in some of the struts does notchange the outer profile of the cage. However, the undulated portions ofthe struts add length to the struts, such that, ceteris paribus, thetotal axially-elongated length of the stent that includes the strutshaving the undulated portions is greater than the totalaxially-elongated length of the stent that does not include the strutshaving the undulated portions.

As described hereinabove, typically, the length of the impeller when theimpeller is in its axially-elongated, crimped configuration is less thanthe length of the cage when the cage is in its axially-elongated,crimped configuration, such that the crimped cage can accommodate theaxially-elongated impeller. In turn, the dimensions of the cage arelimited, since the diameter of the cage in the radially-expandedconfiguration of the cage is limited based upon the size of the bloodvessel into which the blood pump is to be placed. For cages havingstructures as shown in FIG. 17 , then a cage that has a longer crimpedlength, typically expands to have a greater maximum diameter inside theblood vessel, which may be undesirable.

For some applications, in order to increase the axially-elongated lengthof the cage, without increasing the diameter of the cage in theradially-expanded configuration of the cage, a cage as shown FIG. 18C isused. The cage shown in FIG. 18C includes some struts that compriseundulated portions 210. During crimping of the cage, the undulatedportions are configured to become at least partially straightened,thereby adding to the crimped length of the cage relative to if portions210 were not undulated. When the cage radially expands inside the bloodvessel, the undulated portions become undulated, but do not add to thediameter of the cage, or otherwise change the outer profile of the cagerelative to if the undulated portions were straight. Thus, in general,the extra length that is provided to the cage by the undulated portionswhen the cage is in a crimped configuration thereof, does not add to thediameter of the cage when the cage expands inside the blood vessel.

As described, during insertion of the cage into the renal vein, theundulated portions of the struts of the cage are at least partiallystraightened. Upon the cage assuming its radially-expanded configurationinside the renal vein, the level of undulation of the undulated portionsof the struts of the cage increases. For some applications, for each ofthe struts that defines the undulated portions, the strut is configuredsuch that a ratio of:

-   -   (a) the shortest distance from a first longitudinal end of the        strut to a second longitudinal end of the strut when the cage is        its axially-elongated configuration (i.e., when the undulated        portion is at least partially straightened),    -   to    -   (b) the shortest distance from the first longitudinal end of the        strut to the second longitudinal end of the strut when the cage        is its radially-expanded configuration (i.e., when the undulated        portion is at the level of undulation to which the strut was        shape set),    -   is greater than 1.05:1, e.g., greater than 1.15:1, or greater        than 1.2:1.

For some applications, the aforementioned ratio is less than 1.4:1, forexample, the ratio may be between 1.05:1 and 1.4:1, between 1.15:1 and1.4:1, or between 1.2:1 and 1.4:1.

Reference is now made to FIGS. 19A-B, which are schematic illustrationsof impeller cage 154, the cage being shaped to define a central portionhaving a generally cylindrical shape, in the absence of any force beingapplied to the cage, in accordance with some applications of the presentinvention. The outer surface of the cage at the generally cylindricalportion of the cage is parallel to longitudinal axis 222 of the cage.FIG. 19A shows the cage by itself, and FIG. 19B shows the cage disposedinside a blood vessel, e.g., renal vein 32.

FIG. 19B shows cage 154, the cage having radially expanded inside theblood vessel (e.g., inside renal vein 32), such that the cage isanchored to the blood vessel. As described hereinabove, impeller 152 ofblood pump 150 (FIG. 12Ai) is configured to pump blood axially throughthe blood vessel, by rotating inside the blood vessel. Typically, inorder to for the impeller to efficiently pump blood through the bloodvessel, it is desirable that a longitudinal axis 224 of the impeller bealigned with a longitudinal axis 226 of the blood vessel. Furthertypically, rings 164 of impeller 152 are aligned with rings 202 of cage154, such that the longitudinal axes of the impeller and the cage arealigned with one another. For example, as shown in FIG. 12B, thelongitudinal axes of the impeller and the cage may be aligned with oneanother by (a) placing the proximal rings of both the impeller and thecage around a first support element (such as proximal bearing 250P),such that the proximal rings of the impeller and the cage are alignedwith one another, and (b) placing the distal rings of both the impellerand the cage around a second support element (such as distal bearing250D), such that the distal rings of the impeller and the cage arealigned with one another.

As shown in FIG. 19B, generally-cylindrical central portion 220 of cage154, becomes anchored to the blood vessel, such that the longitudinalaxis of the cage is aligned with the longitudinal axis of the bloodvessel. Since the longitudinal axes of the impeller and the cage arealigned with one another, the generally-cylindrical central portion ofthe cage causes the impeller to be disposed within the blood vessel suchthat the longitudinal axis of the impeller is aligned with thelongitudinal axis of the blood vessel.

As used in the present application, including in the claims, a“longitudinal axis” of a structure is the set of all centroids ofcross-sectional sections of the structure along the structure. Thus thecross-sectional sections are locally perpendicular to the longitudinalaxis, which runs along the structure. (If the structure is circular incross-section, the centroids correspond with the centers of the circularcross-sectional sections.)

Reference is now made to FIG. 20 , which is a schematic illustration ofimpeller cage 154, the cage being configured to be placed inside a bloodvessel (e.g., renal vein 32), such as to cause the diameter of a portionof the blood vessel to increase relative to the diameter of the bloodvessel in the absence of the impeller cage. As shown in FIG. 20 , forsome applications the cage is configured to expand a blood vessel thathas a diameter D6 in the absence of the cage, such that a portion of theblood vessel has a diameter that is greater than D6. For example, thecage may widen the blood vessel, such that, when the blood vessel iswidened, the diameter of the blood vessel is more than 105 percent,e.g., more than 110 percent, or more than 115 percent of diameter D6.For some applications, the cage widens the blood vessel, such that, whenthe blood vessel is widened, the diameter of the blood vessel is lessthan 125 percent of diameter D6. For example, the widened diameter maybe 105-125 percent, 110-125 percent, and/or 115-125 percent, of diameterD6. For some applications, impeller 152 of blood pump 150 is configuredto span a diameter that is at least equal to diameter D6 of the bloodvessel. Typically, all other factors being equal, the greater thediameter that the impeller spans, the greater the flow rate at which theimpeller is able to pump blood through the blood vessel.

Reference is now made to FIG. 21A, which is a schematic illustration ofimpeller-based blood pumps 150 inserted into a subject's left and rightrenal veins 32 via the subject's femoral vein 230, in accordance withsome applications of the present invention. It is noted that details ofblood pump 150 are not shown in FIG. 21A, but the pump is generally asdescribed hereinabove. Typically, the blood pumps are inserted into theleft and right renal veins via respective catheters 155, and thecatheters are both inserted via the femoral vein. Alternatively (notshown), the blood pumps are inserted via a single catheter that passesfrom a femoral access point to the subject's vena cava.

Typically, the impellers of the blood pumps 150 are coupled to motors232, which impart rotational motion to the impellers. In accordance withrespective applications, the motors are disposed outside of thesubject's body (as shown) or are placed inside the subject's body (notshown). Typically, a control unit 234 and a user interface 236 aredisposed outside the subject's body. Further typically, the control unitreceives inputs from pressure sensors 157 and 159, which are disposed onupstream and downstream sides of the blood pumps, as describedhereinabove with respect to FIG. 12C-D. When blood pump 150 is disposedinside a renal vein (as shown in FIG. 21A, for example), the pressuremeasured by upstream pressure sensor 157 is indicative of blood pressureupstream of the blood pump, inside the renal vein, and the pressuremeasured by downstream pressure sensor 159 is indicative of centralvenous pressure. For some applications, the control unit receives aninput from additional sensor 161 (such as a flow sensor and/or anoxygen-saturation sensor), which is disposed on the blood pump (e.g., ona downstream side of the blood pump, as shown in FIG. 12Ai).Alternatively or additionally, the control unit receives an input from athermal flow sensor, such as thermal flow sensor 260 describedhereinbelow with reference to FIGS. 22Ai-Cii.

For some applications, control unit 234 controls rotation of impeller152, by controlling motor 232, responsively to one or more of theabove-described inputs. Typically, user interface 236 displays thesubject's current renal venous pressure and central venous pressure,based upon the pressures measured by sensors 157 and 159. Typically,based upon the current values of the subject's renal venous pressure andcentral venous pressure, a user (such as a healthcare professional)inputs a target value for the subject renal venous pressure, via theuser interface. In response thereto, control unit 234 controls the speedof the rotation of the impeller, such that the impeller pumps throughthe renal vein and toward the vena cava at a flow rate that is such asto reduce the renal venous pressure toward the target level, asindicated by the user. For some applications, in response a signalreceived from downstream sensor 159 indicating that the central venouspressure is at the target renal venous pressure, the control unit stopsthe impeller rotating. In general, the control unit typically controlsthe speed of the rotation of the impeller responsively to inputs frompressure sensors 157 and 159. For some applications, the control unitcontrols the speed of the rotation of the impeller responsively to aninput from additional sensor 161, and/or thermal flow sensor 260 (shownin FIGS. 22Ai-22Cii).

It is noted that a “control unit” as described in the presentapplication, in the description and the claims, includes any type ofprocessor (such as a computer processor) configured to execute theactions described herein. A “user interface” includes any type of userinterface configured to receive inputs from a user and/or to provideoutputs to the user. For example, the user interface may include one ormore input devices (such as a keyboard, a mouse, a trackball, ajoystick, a touchscreen monitor, a touchpad, a voice-command interface,a smartphone, a tablet computer, and/or other types of input devicesthat are known in the art), and/or one or more output devices (such as amonitor, an audio output device, a smartphone, a tablet computer, and/orother types of output devices that are known in the art).

Reference is now made to FIG. 21B, which is a schematic illustration ofimpeller-based blood pumps 150 inserted into a subject's left and rightrenal veins 32 via the subject's subclavian vein 240, in accordance withsome applications of the present invention. It is noted that the detailsof blood pump 150 are not shown in FIG. 21B, but the pump is generallyas described hereinabove. Typically, the blood pumps are inserted intothe left and right renal veins via respective catheters, and thecatheters are both inserted via the subclavian vein. Alternatively (notshown), the blood pumps are inserted via a single catheter then passesfrom a subclavian access point to the subject's vena cava. Apart frombeing inserted into the renal veins via a different vein, blood pumps150 as shown in FIG. 21B are generally similar to blood pumps 150 asshown in FIG. 21A, in all other respects.

Reference is now made to FIGS. 22Ai-Cii, which are schematicillustrations of a thermal flow sensor 260 for use with blood pump 150,in accordance with some applications of the present invention. Thethermal flow sensor typically includes an upstream temperature sensor262, a downstream temperature sensor 264, and a heating element 266disposed between the upstream and downstream temperature sensors. Asshown by the flow arrows shown in the enlarged drawing of the thermalflow sensor in FIG. 22Ai, blood flows past the upstream temperaturesensor to the heating element. The heating element heats the blood, asthe blood flows past the heating element. The heated blood then flows tothe downstream temperature sensor. The extent to which blood flowingpast the downstream temperature sensor has been heated by the heatingelement is dependent upon the flow rate of the blood. Therefore, thethermal flow sensor measures a change in the temperature of the bloodbetween the upstream and the downstream temperature sensors, anddetermines the flow of the blood responsively thereto.

As described with reference to FIGS. 21A-B, for some applications, thecontrol unit controls the speed of the rotation of the impellerresponsively to an input from thermal flow sensor 260. Typically, it isof interest to measure the component of the blood flow through the renalvein that is in the axial direction, i.e., the axial component of theblood flow that is parallel to the local longitudinal axis of the renalvein, since this determines the rate of flow of blood away from thesubject's kidney. However, due to the rotation of the impeller, bloodflow downstream of the impeller typically includes components other thanthe axial component (e.g., rotational and radial components). For someapplications, the thermal flow sensor is disposed inside a housing 268that is configured such that blood flow through housing is substantiallyin the axial direction, and such that components other than the axialcomponent of the blood flow (e.g., rotational and radial components) arereduced relative to blood flow through the renal vein outside thehousing.

Reference is now made to FIGS. 22Ai and 22Aii, which are schematicillustrations of, respectively, a cross-sectional view and a top view ofthermal flow sensor 260 and housing 268, in accordance with someapplications of the present invention. Typically, impeller 152 and cage154 of blood pump 150 are disposed at the end of an elongate element 270(e.g., a tube) of the blood pump. For some applications, elongateelement 270 defines an indentation, and the thermal flow sensor ishoused inside the indentation, the outer surface of elongate element 270that defines the indentation thus comprising housing 268. Upstreamtemperature sensor 262, heating element 266, and downstream temperaturesensor 264 are typically disposed sequentially along the length of theindentation, as shown. Typically, the ratio of length LI of theindentation to a width WI of the indentation is greater than 4:1, and/orless 8:1, e.g., between 4:1 and 8:1. The ratio of length LI to width WIis typically such that blood flow through the indentation issubstantially in the direction that is parallel to the locallongitudinal axis of the renal vein (and that is parallel to the locallongitudinal axis of the elongate element), and such that componentsother than the axial component of the blood flow (e.g., rotational andradial components) are reduced relative to blood flow through the renalvein outside the housing. Since the thermal sensor is housed inside theindentation, the thermal flow sensor measures the blood flow that issubstantially in the direction that is parallel to the locallongitudinal axis of the renal vein (and that is parallel to the locallongitudinal axis of the elongate element).

For some applications (not shown), a single thermistor is used tomeasure flow, and the single thermistor is placed inside a housing thatis typically such that blood flow through the housing is substantiallyin the direction that is parallel to the local longitudinal axis of therenal vein (and that is parallel to the local longitudinal axis of theelongate element), and such that components other than the axialcomponent of the blood flow (e.g., rotational and radial components) arereduced relative to blood flow through the renal vein outside thehousing, e.g., using techniques as described with respect to FIGS.22Ai-22Cii, mutatis mutandis. For such applications, a ratio of a lengthof the housing to the width of the housing is typically greater than1:1, e.g., greater than 4:1, and/or less 8:1, e.g., between 4:1 and 8:1.For such applications, when a housing as shown in FIG. 22Ci-ii is used,the ratio of the length of the housing to the height of the housing istypically greater than 1:1, e.g., greater than 4:1, and/or less 8:1,e.g., between 4:1 and 8:1.

Reference is now made to FIGS. 22Bi and 22Bii, which are schematicillustrations of, respectively, a cross-sectional view and a top view ofthermal flow sensor 260 and housing 268, in accordance with someapplications of the present invention. Housing 268 as shown in FIGS.22Bi-22Bii is generally similar to that shown in FIGS. 22Ai-22Aii,except that the thermal sensor shown in FIGS. 22Bi-ii in covered by acover 272 in addition to being housed inside the indentation in elongateelement 270. In other aspects, thermal sensor and housing 268 aregenerally as described with reference to FIGS. 22Ai-22Aii.

Reference is now made to FIGS. 22Ci-22Cii, which are schematicillustrations of respective cross-sectional views of thermal flow sensor260 and housing 268, in accordance with some applications of the presentinvention. For some applications, housing 268, which houses thermalsensor 260, includes a housing, such as a tube, that is coupled to theouter surface of elongate element 270 of blood pump 150. Typically, thehousing is compressible, such that the housing may be compressed duringinsertion of blood pump 150 into the subject's blood vessel viainsertion device 155.

Upstream temperature sensor 262, heating element 266, and downstreamtemperature sensor 264 are typically disposed sequentially along thelength of the housing, within the housing, as shown. Typically, theratio of a length LH of the housing to a width WH of the housing isgreater than 4:1, and/or less 8:1, e.g., between 4:1 and 8:1. Furthertypically, the ratio of a length LH of the housing to a height HH of thehousing is greater than 4:1, and/or less 8:1, e.g., between 4:1 and 8:1.The ratios of length LH to width WH, and of length LH to height HH, aretypically such that blood flow through the housing is substantially inthe direction that is parallel to the local longitudinal axis of therenal vein (and that is parallel to the local longitudinal axis of theelongate element), and such that components other than the axialcomponent of the blood flow (e.g., rotational and radial components) arereduced relative to blood flow through the renal vein outside thehousing. Since the thermal sensor is housed inside the indentation, thethermal flow sensor measures the blood flow that is substantially in thedirection that is parallel to the local longitudinal axis of the renalvein (and that is parallel to the local longitudinal axis of theelongate element).

It is noted that in FIG. 22Cii, the inside of elongate element 270 isshaded, for illustrative purposes. However, typically, elongate element270 houses control mechanisms for controlling motion of impeller 152 andcage 154.

Experimental Results

Reference is now made to FIG. 23 , which shows graphs indicating theresults of experiments that were performed on a healthy pig, using animpeller-based blood pump 150, in accordance with some applications ofthe present invention. Throughout the experiment, left renal venouspressure of the pig was measured directly using a pressure sensordisposed in the pig's left renal vein. In addition, right renal venouspressure of the pig was measured, using a pressure sensor in theinferior vena cava at the level of the renal vein. Baseline levels ofleft renal blood flow, and urine output from the left and right kidneyswere also measured, and the aforementioned parameters were againmeasured at certain points in time during the experiment.

A balloon was inflated in the pig's vena cava downstream of thejunctions between the vena cava and both left and right renal veins. Theballoon was inflated such as to cause an increase in the blood pressurewithin the pig's vena cava downstream of the renal veins, by partiallyobstructing blood flow through the vena cava downstream of the renalveins. At the same time as the balloon was inflated inside the pig'svena cava, an impeller-based blood pump, as described herein, wasactivated to pump blood through the pig's left renal vein, while noassistance was provided to the flow of blood through the pig's rightrenal vein. While the balloon was still in an inflated state, the bloodpump within the left renal vein was temporarily switched off for aperiod of time, before being switched on again. Subsequently, theballoon within the vena cava was deflated, and the blood pump wasswitched off.

The top graph in FIG. 23 indicates left renal venous pressure, indicatedby the solid curve, and right renal venous pressure, indicated by thedashed curve, as measured during the experiment. It is noted that, inorder to more clearly show the left and right renal venous pressuremeasurements, where the left and right renal venous pressuremeasurements were identical (e.g., between approximately 12:35 and13:28), the two curves have been separated slightly. In addition smallvariations in venous pressure have been ignored. As shown, initially,during the baseline period, the left and right renal venous pressureswere similar to one another, at approximately 8 mmHg. Subsequently, at13:28, the balloon was inflated, and the impeller-based blood pump wasactivated in the left renal vein. As a result of the balloon beinginflated, the pressure in the vena cava rose, and therefore the rightrenal venous pressure rose to approximately 22 mmHg. Despite thepressure in the vena cava rising, the left renal venous pressure did notincrease, due to the pumping of blood through the left renal vein. Atapproximately 14:10, the blood pump within the left renal vein wasswitched off, and, as a result, the left renal venous pressure rose tothe level of the venous pressure within the vena cava. Subsequently, atapproximately 14:40, the pump was switched on again, and, as a result,the pressure in the left renal vein dropped. Subsequently, at 15:24, theballoon was deflated and the venous pressure in the vena cava, andtherefore, the right renal venous pressure dropped. These resultsindicate that an impeller-based blood pump as described herein mayeffectively reduce renal venous pressure, even if a subject's centralvenous pressure is elevated.

The middle graph of FIG. 23 shows the renal blood flow as measured inthe left renal vein. As shown the baseline value of the left renal bloodflow was approximately 360 ml/min. The left renal blood flow was againmeasured when the balloon had been inflated in the vena cava and theblood pump was operating in the left renal vein. As shown, left renalblood flow had risen to approximately 440 ml/min, due to the pumping ofthe blood by the blood pump. Subsequently, left renal blood flow wasmeasured while the balloon was inflated within the vena cava, and whilethe blood pump had been switched off, and the renal blood flow hadfallen to approximately 380 ml/min. Subsequently, left renal blood flowwas again measured when the blood pump had been switched back on, andthe left renal blood flow had again risen to approximately 340 ml/min.These results indicate that an impeller-based blood pump as describedherein may effectively increase renal blood flow, even if a subject'scentral venous pressure is elevated.

It is noted that, for illustrative purposes, changes in renal blood flowbetween one data point and the next data point are shown on the graph ashaving occurred at a constant rate. However, the inventors hypothesizethat the changes in renal blood flow were substantially due to the bloodpump being switched on and off inside the left renal vein, and/or due toinflation of the balloon inside the vena cava, such that most of thechanges in the renal blood flow would have occurred, pursuant to theoccurrences of the aforementioned events.

The bottom graph of FIG. 23 shows urine output measured at the pig'sleft kidney (indicated by the solid curve) and right kidney (indicatedby the dashed curve) at certain times during the experiment. It is notedthat, in general, it is known that the rate of blood flow through thekidney has an effect on the rate of urine output. As shown, whenmeasured during the baseline period, urine production from the left andright kidneys was approximately 21 ml per 10 minutes. Subsequently,urine output was measured at approximately 14:00, while the balloon wasinflated inside the vena cava, and while the blood pump was operatinginside the left renal vein. As shown, urine output from the left kidneyhad risen, while urine production from the right kidney had fallen.These results indicate that, even when central venous pressure iselevated, which may lead to reduced urine output (as indicated by theurine output from the right kidney), increasing renal blood flow bypumping blood using a blood pump (as performed within the left renalvein) may increase urine output.

Subsequently, urine output from the left and right kidneys was measuredwhile the balloon was still inflated inside the vena cava, but while theblood pump was switched off, at approximately 14:35. At this point,urine production at the right kidney had continued to fall, while urineoutput from the left kidney had also fallen. Subsequently, after theblood pump had been switched on again, while the vena cava balloon hadstill been inflated, the urine output from the right kidney hadplateaued at approximately 14 ml per 10 minutes, while the urine outputfrom the right kidney had risen substantially to 48 ml per 10 minutes.

It is noted that, for illustrative purposes, changes in urine productionbetween one data point and the next data point are shown on the graph ashaving occurred at a constant rate. However, the inventors hypothesizethat the changes in urine production were substantially due to the bloodpump being switched on and off inside the left renal vein, and/or due toinflation of the balloon inside the vena cava, such that most of thechanges in the urine production would have occurred, pursuant to theoccurrences of the aforementioned events.

In a further experiment, an impeller-based blood pump as describedherein was used to pump blood through the renal vein of a different pigover a continuous period of three hours. During this time period, noincidences of either thrombi, or abnormal levels of hemolysis occurred.This indicates that an impeller-based blood pump as described herein maybe used to increase blood flow through a subject's renal vein, therebyreducing pressure in renal vein, without causing a risk of thrombiand/or abnormal levels of hemolysis. It is noted that during theaforementioned experiment, an anticoagulant was administered to the pig.Nevertheless, since in a typically procedure that is performed on ahuman subject using an impeller-based blood pump as described herein,the subject would be administered an anticoagulant, it is still the casethat this result indicates that an impeller-based blood pump asdescribed herein may be used to increase blood flow through a subject'srenal vein, thereby reducing pressure in renal vein, without causing arisk of hemolysis and/or thrombi.

In general, in the above-described experiments, as well as in additionalexperiments that were performed by the inventors of the presentapplication using blood pump 150 in pigs, the following observationswere made:

-   -   1. Blood pump 150 was smoothly deployed and retrieved within a        minute or less.    -   2. Renal venous pressure was effectively and continuously        reduced from about 20 mmHg to a pre-selected target value of 8        mmHg within minimal margins of variation.    -   3. Elevation of venous pressure in the vena cava caused a drop        in urine output, creatinine clearance, and fractional sodium        excretion in the untreated kidney, but not in the kidney that        was treated using blood pump 150. These results indicate that        use of blood pump 150 has a favorable impact on glomerular and        tubular renal function.    -   4. Use of blood pump 150 preserved and restored renal blood        flow, urine output, and sodium excretion, even when venous        pressure in the vena cava was elevated.    -   5. Blood pump 150 was successfully operated in a closed-looped        mode, under which pressure in the renal vein was kept constant        for more than 3 hours.    -   6. No thrombi were observed on any part of the blood pump, or        the catheter.    -   7. No clinically significant hemolysis was observed over 3 hours        of the pump being operated.

It is noted that although some of the pumps and/or occlusion elementsdescribed herein are shown as being inserted into a given one of thesubject's renal veins, the scope of the present invention includesinserting the pumps and occlusion elements into either a left or rightrenal vein, or both renal veins of a subject. Furthermore the scope ofthe present invention includes inserting the pumps and occlusionelements into more than two renal veins of a subject who has more thantwo renal veins, as is the case with some people.

It is noted that although some of the pumps and/or occlusion elementsdescribed herein are shown as being inserted into subject's renal veins,the scope of the present invention includes inserting the pumps andocclusion elements into other blood vessels of a subject, mutatismutandis. For example, inverted valve 40 (FIGS. 5A-D, and 6A-F) could beplaced in a subject's hepatic vein, intestinal vein, or adrenal vein, inorder to reduce venous pressure in the vein and/or reduce pressure in anorgan from which the vein draws blood (e.g., to reduce livercongestion).

Alternatively or additionally, blood pump 90 (FIGS. 8A-B and 10A-D)could be placed in a subject's hepatic vein, intestinal vein, or adrenalvein, in order to reduce venous pressure in the vein and/or reducepressure in an organ from which the vein draws blood (e.g., to reduceliver congestion). Or, blood pump 90 could be placed in a fluid-filledchamber inside the brain in order to reduce intracranial pressure bydraining cerebrospinal fluid from the chamber. Alternatively oradditionally, blood pump 90 could be used as a left ventricular assistdevice by being placed in the subject's aorta and pumping blood awayfrom the left ventricle. Further alternatively or additionally, bloodpump 90 could be placed in the urethra, such as to hold open thesubject's prostate, and to drain the subject's bladder.

In general, sleeve 110 (FIGS. 10A-C) may be used to isolate into aseparate compartment from blood flow within a main vein, blood that iswithin a plurality of tributary veins that supply the main vein, andpump 122 may then be used to control the flow of blood from thecompartment to the main vein.

For some applications, ostium-covering umbrella 140 (FIGS. 11A-C) isused to cover an ostium at a junction between a subject's hepatic vein,intestinal vein, or adrenal vein and another vein, and blood pumpcatheter 42 is used to control the flow of blood from the hepatic vein,intestinal vein, or adrenal vein to the other vein, in order to reducevenous pressure in the vein and/or reduce pressure in an organ fromwhich the vein draws blood (e.g., to reduce liver congestion).

For some applications, blood pump 150 (FIGS. 12Ai-E) is placed in anartery that supplies a peripheral limb such as to enhance perfusion ofthe peripheral limb, for example in order to treat a gangrenous limb.Alternatively or additionally, a blood pump, such as blood pump 150 isplaced in an artery, such as the descending aorta in order to propelblood away from the heart, such as to reduce afterload, and/or otherwiseimprove cardiac function.

In general, in the specification and in the claims of the presentapplication, the term “proximal” and related terms, when used withreference to a device or a portion thereof, should be interpreted tomean an end of the device or the portion thereof that, when insertedinto a subject's body, is typically closer to a location through whichthe device is inserted into the subject's body. The term “distal” andrelated terms, when used with reference to a device or a portionthereof, should be interpreted to mean an end of the device or theportion thereof that, when inserted into a subject's body, is typicallyfurther from the location through which the device is inserted into thesubject's body.

In general, in the specification and in the claims of the presentapplication, the term “downstream” and related terms, when used withreference to a blood vessel, or with reference to a portion of a devicethat is configured to be placed inside a blood vessel, should beinterpreted to mean a location within the blood vessel, or a portion ofthe device that is intended for placement at a location within the bloodvessel, that is downstream, with respect to the direction of antegradeblood flow through the blood vessel, relative to a different locationwithin the blood vessel. The term “upstream” and related terms, whenused with reference to a blood vessel, or with reference to a portion ofa device that is configured to be placed inside a blood vessel, shouldbe interpreted to mean a location within the blood vessel, or a portionof the device that is intended for placement at a location within theblood vessel, that is upstream with respect to the direction ofantegrade blood flow through the blood vessel, relative to a differentlocation within the blood vessel.

There is therefore provided the following inventive concepts, inaccordance with some applications of the present invention:

Inventive concept 1. A method for use with a plurality of tributaryveins that supply a main vein, comprising:

-   -   mechanically isolating blood within the plurality of veins into        a compartment that is separated from blood flow within the main        vein; and    -   controlling blood flow from the plurality of veins to the major        vein by pumping blood from the compartment to the main vein.        Inventive concept 2. The method according to inventive concept        1, further comprising performing ultrafiltration on the pumped        blood.        Inventive concept 3. The method according to inventive concept        1,    -   wherein isolating the plurality of veins comprises:        -   placing into the main vein a blood-impermeable sleeve and a            helical support element disposed around the sleeve, and        -   coupling the sleeve to a wall of the main vein using the            helical support element; and    -   wherein pumping blood from the compartment to the main vein        comprises guiding a distal portion of a blood pump into the        compartment using the helical support element and pumping the        blood using the blood pump.        Inventive concept 4. The method according to inventive concept        1, wherein:    -   isolating the plurality of veins comprises:        -   placing into the main vein a blood-impermeable sleeve and a            helical portion of a blood pump that is disposed around the            sleeve and configured to support the sleeve, and        -   coupling the sleeve to a wall of the main vein; and    -   pumping blood from the compartment to the main vein comprises        pumping blood into inlet holes of the blood pump that are        defined by the helical portion of the blood pump.        Inventive concept 5. The method according to any one of        inventive concepts 1-4, wherein:    -   isolating blood within the plurality of veins into a compartment        that is separated from blood flow within the main vein comprises        isolating blood in renal veins of the subject into a compartment        that is separated from blood flow within a vena cava of the        subject by placing a blood-impermeable sleeve in the subject's        vena cava, such that a downstream end of the sleeve is coupled        to a wall of the vena cava at a first location that is        downstream of all of the renal veins of the subject, and such        that an upstream end of the sleeve is coupled to the wall of the        vena cava at a second location that is upstream of all the renal        veins of the subject; and    -   pumping blood from the compartment to the main vein comprises        operating a pump to pump blood from the compartment to a        location that is in fluid communication with an interior of the        sleeve.        Inventive concept 6. The method according to inventive concept        5, wherein pumping blood from the compartment comprises drawing        blood in a downstream direction through the renal veins.        Inventive concept 7. The method according to inventive concept        5, wherein placing the sleeve in the vena cava comprises placing        the sleeve in the vena cava for less than one week, and wherein        operating the pump comprises operating the pump for less than        one week.        Inventive concept 8. The method according to inventive concept        5, further comprising identifying the subject as a subject        suffering from a condition selected from the group consisting        of: cardiac dysfunction, congestive heart failure, reduced renal        blood flow, increased renal vascular resistance, arterial        hypertension, and kidney dysfunction, and wherein operating the        pump comprises, in response to identifying the subject as        suffering from the condition, reducing blood pressure within the        subject's renal veins by operating the pump.        Inventive concept 9. The method according to inventive concept        5, wherein placing the sleeve in the subject's vena cava        comprises anchoring the sleeve to the vena cava by causing the        vena cava to constrict around at least a portion of the sleeve,        by operating the pump.        Inventive concept 10. The method according to inventive concept        5, wherein operating the pump to pump blood from the compartment        to the location that is in fluid communication with an interior        of the sleeve comprises operating the pump to pump blood from        the compartment to a site of the vena cava that is upstream of        the sleeve.        Inventive concept 11. The method according to inventive concept        5, wherein operating the pump to pump blood from the compartment        to the location that is in fluid communication with an interior        of the sleeve comprises operating the pump to pump blood from        the compartment to a site of the vena cava that is downstream of        the sleeve.        Inventive concept 12. The method according to inventive concept        5, wherein placing the sleeve in the vena cava comprises placing        into the vena cava:    -   a stent shaped to define widened upstream and downstream ends        thereof that are widened relative to a central portion of the        stent, and    -   a blood-impermeable sleeve coupled to the stent, the sleeve        defining flared upstream and downstream ends thereof that are        coupled, respectively, to the widened upstream and downstream        ends of the stent; and    -   coupling the stent to the blood vessel such that:        -   in response to blood pressure on a first side of at least            one of the flared ends of the sleeve being greater than            blood pressure on a second side of the at least one flared            end of the sleeve, blood flows between an outside of the at            least one flared end of the sleeve and an inner wall of the            blood vessel, and        -   in response to blood pressure on the first side of the at            least one flared end of the sleeve being less than blood            pressure on the second side of the at least one flared end            of the sleeve, the at least one flared end of the sleeve            occludes blood flow between the outside of the at least one            flared end of the sleeve and the inner wall of the blood            vessel by contacting the inner wall of the blood vessel.            Inventive concept 13. The method according to inventive            concept 5, wherein placing the sleeve in the vena cava            comprises placing into the vena cava:    -   a sleeve that is shaped to define flared ends thereof, and a        narrow central portion between the flared ends, and    -   a stent shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.            Inventive concept 14. The method according to inventive            concept 13, wherein pumping blood from the compartment            comprises pumping blood from a site between an outside of            the sleeve and an inner wall of the vena cava.            Inventive concept 15. The method according to inventive            concept 5, further comprising inserting the pump into the            compartment via an opening in the sleeve through which the            pump is insertable.            Inventive concept 16. The method according to inventive            concept 15, wherein inserting the pump through the opening            comprises inserting the pump through an opening having a            diameter that is between 2 mm and 10 mm.            Inventive concept 17. The method according to inventive            concept 15, wherein inserting the pump through the opening            comprises inserting the pump through the opening such that            the opening forms a seal around the pump.            Inventive concept 18. The method according to inventive            concept 5, further comprising inserting the pump into the            compartment via a pump-accommodating sleeve that protrudes            from the sleeve.            Inventive concept 19. The method according to inventive            concept 18, wherein inserting the pump into the compartment            via the pump-accommodating sleeve comprises inserting the            pump into the compartment via a pump-accommodating sleeve            having a diameter that is between 2 mm and 10 mm.            Inventive concept 20. The method according to inventive            concept 18, wherein inserting the pump into the compartment            via the pump-accommodating sleeve comprises inserting the            pump into the compartment via the pump-accommodating sleeve            such that the pump-accommodating sleeve forms a seal around            the pump.            Inventive concept 21. Apparatus, comprising:    -   a blood-impermeable sleeve;    -   at least one support structure configured to couple first and        second ends of the sleeve to a blood vessel of a subject; and    -   a pump configured to pump blood from an exterior of the sleeve        to a location that is in fluid communication with an interior of        the sleeve.        Inventive concept 22. The apparatus according to inventive        concept 21, wherein the pump is configured to perform        ultrafiltration on the blood.        Inventive concept 23. The apparatus according to inventive        concept 21, wherein the pump is configured to anchor the        structure to the blood vessel by causing the blood vessel to        constrict around at least a portion of the structure.        Inventive concept 24. The apparatus according to inventive        concept 21,    -   wherein the structure comprises a stent shaped to define widened        ends thereof that are widened relative to a central portion of        the stent, and    -   wherein the sleeve comprises a sleeve that is coupled to the        stent,        -   the sleeve defining flared ends thereof that are coupled to            the widened ends of the stent,        -   at least one of the flared ends of the sleeve being            configured to act as a valve by at least partially            separating from widened end of the stent to which it is            coupled in response to pressure being applied to the flared            end of the sleeve.            Inventive concept 25. The apparatus according to inventive            concept 21, wherein:    -   the support structure comprises a helical support element        disposed around the sleeve, and    -   a distal portion of the blood pump is configured to be guided        such as to be disposed around the exterior of the sleeve using        the helical support element.        Inventive concept 26. The apparatus according to inventive        concept 21, wherein:    -   the support structure comprises a helical portion of the blood        pump that is disposed around the sleeve and configured to        support the sleeve, and    -   the pump is configured to pump blood from the exterior of the        sleeve by pumping blood into inlet holes of the pump that are        defined by the helical portion of the blood pump.        Inventive concept 27. The apparatus according to any one of        inventive concepts 21-24, wherein:    -   the sleeve is shaped to define flared ends thereof, and a narrow        central portion between the flared ends;    -   the structure comprises a stent shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.            Inventive concept 28. The apparatus according to inventive            concept 27, wherein the pump is configured to pump blood            from a site between an outside of the sleeve and an inner            wall of the blood vessel by being placed between the outside            of the sleeve and the vessel-wall-supporting frame.            Inventive concept 29. The apparatus according to any one of            inventive concepts 21-26, wherein the structure is            configured to isolate blood in a renal vein of the subject            into a compartment that is separated from blood flow within            a vena cava of the subject, by coupling a downstream end of            the sleeve to a wall of the vena cava at a first location            that is downstream of all renal veins of the subject, and by            coupling an upstream end of the sleeve to a wall of the vena            cava at a second location that is upstream of all renal            veins of the subject.            Inventive concept 30. The apparatus according to inventive            concept 29, wherein the sleeve is configured to be coupled            to the vena cava for less than one week, and wherein the            pump is configured to operate for less than one week.            Inventive concept 31. The apparatus according to inventive            concept 29, wherein the pump is configured to reduce blood            pressure within the subject's renal veins by pumping blood.            Inventive concept 32. The apparatus according to inventive            concept 29, wherein the pump is configured to pump blood            from the compartment to a site within the vena cava.            Inventive concept 33. The apparatus according to inventive            concept 32, wherein the pump is configured to pump blood            from the compartment to a site of the vena cava that is            upstream of the sleeve.            Inventive concept 34. The apparatus according to inventive            concept 32, wherein the pump is configured to pump blood            from the compartment to a site of the vena cava that is            downstream of the sleeve.            Inventive concept 35. The apparatus according to any one of            inventive concepts 21-26, wherein the sleeve is shaped to            define an opening through which the pump is insertable.            Inventive concept 36. The apparatus according to inventive            concept 35, wherein a diameter of the opening is between 2            mm and 10 mm.            Inventive concept 37. The apparatus according to inventive            concept 35, wherein the opening is sized such as to form a            seal around the pump.            Inventive concept 38. The apparatus according to any one of            inventive concepts 21-26, further comprising a            pump-accommodating sleeve protruding from the            blood-impermeable sleeve, the pump accommodating sleeve            being configured to accommodate insertion of the pump            therethrough to the exterior of the blood impermeable            sleeve.            Inventive concept 39. The apparatus according to inventive            concept 38, wherein an inner diameter of the            pump-accommodating sleeve is between 2 mm and 10 mm.            Inventive concept 40. The apparatus according to inventive            concept 38, wherein the pump-accommodating sleeve is sized            such as to form a seal around the pump.            Inventive concept 41. A method comprising:    -   placing a stent inside a blood vessel at a placement location of        the stent; and    -   at least partially anchoring the stent to the blood vessel at        the placement location by causing the blood vessel to constrict        around at least a portion of the stent, by applying a suctioning        force within the blood vessel.        Inventive concept 42. The method according to inventive concept        41, wherein the blood vessel includes a blood vessel having a        given diameter at the placement location, and wherein placing        the stent inside the blood vessel comprises placing inside the        blood vessel a stent having a diameter that is less than the        given diameter.        Inventive concept 43. The method according to inventive concept        41, wherein causing the blood vessel to constrict around at        least the portion of the stent comprises reducing an extent to        which the stent is anchored to the blood vessel by virtue of        oversizing of the stent, relative to if the blood vessel were        not caused to constrict around at least the portion of the        stent.        Inventive concept 44. Apparatus comprising:    -   a stent configured to be placed inside a blood vessel at a        placement location of the stent;    -   a pump configured to anchor the stent to the blood vessel at the        placement location by causing the blood vessel to constrict        around at least a portion of the stent, by applying a suctioning        force within the blood vessel.        Inventive concept 45. The apparatus according to inventive        concept 44, wherein the blood vessel includes a blood vessel        having a given diameter at the placement location, and wherein        the stent comprises a stent having a diameter that is less than        the given diameter.        Inventive concept 46. Apparatus comprising:    -   a stent configured to be placed inside a blood vessel, the stent        being shaped to define widened ends thereof that are widened        relative to a central portion of the stent; and    -   a blood-impermeable sleeve coupled to the stent,        -   the sleeve defining flared ends thereof that are coupled to            the widened ends of the stent,        -   at least one of the flared ends of the sleeve being            configured to act as a valve by at least partially            separating from widened end of the stent to which it is            coupled in response to pressure being applied to the flared            end of the sleeve.            Inventive concept 47. A method comprising:    -   placing into a blood vessel of a subject:        -   a stent shaped to define widened upstream and downstream            ends thereof that are widened relative to a central portion            of the stent, and        -   a blood-impermeable sleeve coupled to the stent, the sleeve            defining flared upstream and downstream ends thereof that            are coupled, respectively, to the widened upstream and            downstream ends of the stent; and    -   coupling the stent to the blood vessel such that:        -   in response to blood pressure on a first side of at least            one of the flared ends of the sleeve being greater than            blood pressure on a second side of the at least one flared            end of the sleeve, blood flows between an outside of the at            least one flared end of the sleeve and an inner wall of the            blood vessel, and        -   in response to blood pressure on the first side of the at            least one flared end of the sleeve being less than blood            pressure on the second side of the at least one flared end            of the sleeve, the at least one flared end of the sleeve            occludes blood flow between the outside of the at least one            flared end of the sleeve and the inner wall of the blood            vessel by contacting the inner wall of the blood vessel.            Inventive concept 48. Apparatus comprising:    -   a blood-impermeable sleeve defining flared ends thereof, and a        narrow central portion between the flared ends; and    -   a stent configured to be placed inside a blood vessel, the stent        being shaped to define:        -   a sleeve-supporting frame that is shaped to define widened            ends thereof, and a narrow central portion between the            widened ends that is narrower than the widened ends of the            stent, the sleeve being coupled to the sleeve-supporting            frame of the stent; and        -   a vessel-wall-supporting frame coupled to the narrow central            portion of the sleeve-supporting frame and radially            protruding from the sleeve-supporting frame.            Inventive concept 49. The apparatus according to inventive            concept 48, further comprising a blood pump, the blood pump            being configured to pump blood from between an outside of            the sleeve and an inner wall of the blood vessel by being            placed between the outside of the sleeve and the            vessel-wall-supporting frame.            Inventive concept 50. The apparatus according to inventive            concept 48, wherein a diameter of the narrow central portion            of the sleeve is between 8 mm and 35 mm.            Inventive concept 51. The apparatus according to inventive            concept 48, wherein a maximum diameter of the flared ends of            the sleeve is between 10 mm and 45 mm.            Inventive concept 52. The apparatus according to inventive            concept 48, wherein a ratio of a maximum diameter of the            flared ends of the sleeve, and a diameter of the narrow            central portion of the sleeve is between 1.1:1 and 2:1.            Inventive concept 53. The apparatus according to inventive            concept 48, wherein a maximum diameter of the            vessel-wall-supporting frame is between 10 mm and 50 mm.            Inventive concept 54. The apparatus according to any one of            inventive concepts 48-53, wherein a ratio of a maximum            diameter of the wall-supporting frame to a diameter of the            narrow central portion of the sleeve-supporting frame is            between 1.1:1 and 5:1.            Inventive concept 55. The apparatus according to inventive            concept 54, wherein the ratio is greater than 1.5:1.            Inventive concept 56. The apparatus according to any one of            inventive concepts 48-53, wherein a length of the sleeve is            greater than 6 mm.            Inventive concept 57. The apparatus according to inventive            concept 56, wherein the length of the sleeve is less than 80            mm.            Inventive concept 58. The apparatus according to inventive            concept 56, wherein a length of each one of the flared ends            of the sleeve is greater than 3 mm.            Inventive concept 59. The apparatus according to inventive            concept 58, wherein the length of each one of the flared            ends of the sleeve is less than 40 mm.            Inventive concept 60. The apparatus according to inventive            concept 56, wherein a length of the narrow central portion            of the sleeve is greater than 3 mm.            Inventive concept 61. The apparatus according to inventive            concept 60, wherein the length of the narrow central portion            of the sleeve is less than 70 mm.            Inventive concept 62. A method comprising:    -   placing into a blood vessel of a subject:        -   a blood-impermeable sleeve defining flared ends thereof, and            a narrow central portion between the flared ends, and        -   a stent shaped to define:            -   a sleeve-supporting frame that is shaped to define                widened ends thereof, and a narrow central portion                between the widened ends that is narrower than the                widened ends, the sleeve being coupled to the                sleeve-supporting frame of the stent; and            -   a vessel-wall-supporting frame coupled to the narrow                central portion of the sleeve-supporting frame and                radially protruding from the sleeve-supporting frame;                and    -   coupling the stent to the blood vessel such that the        vessel-wall-supporting frame of the stent holds open the blood        vessel by supporting the wall of the blood vessel, and the        sleeve-supporting frame supports the sleeve within the blood        vessel.        Inventive concept 63. The method according to inventive concept        62, further comprising pumping blood from a site between an        outside of the sleeve and an inner wall of the blood vessel by        placing a pump between the outside of the sleeve and the        vessel-wall-supporting frame.        Inventive concept 64. The method according to inventive concept        62, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, a diameter of the        narrow central portion of the sleeve being between 8 mm and 35        mm.        Inventive concept 65. The method according to inventive concept        62, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, a maximum diameter of        the flared ends of the sleeve being between 10 mm and 45 mm.        Inventive concept 66. The method according to inventive concept        62, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, a ratio of a maximum        diameter of the flared ends of the sleeve, and a diameter of the        narrow central portion of the sleeve being between 1.1:1 and        2:1.        Inventive concept 67. The method according to inventive concept        62, wherein placing the stent into the blood vessel comprises        placing the stent into the blood vessel, a maximum diameter of        the vessel-wall-supporting frame being between 10 mm and 50 mm.        Inventive concept 68. The method according to any one of        inventive concepts 62-67, wherein placing the stent into the        blood vessel comprises placing the stent into the blood vessel,        a ratio of a maximum diameter of the wall-supporting frame to a        diameter of the narrow central portion of the sleeve-supporting        frame being between 1.1:1 and 5:1.        Inventive concept 69. The method according to inventive concept        68, wherein placing the stent into the blood vessel comprises        placing the stent into the blood vessel, the ratio being greater        than 1.5:1.        Inventive concept 70. The method according to any one of        inventive concepts 62-67, wherein placing the sleeve into the        blood vessel comprises placing the sleeve into the blood vessel,        a length of the sleeve being greater than 6 mm.        Inventive concept 71. The method according to inventive concept        70, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, the length of the        sleeve being less than 80 mm.        Inventive concept 72. The method according to inventive concept        70, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, a length of each one        of the flared ends of the sleeve being greater than 3 mm.        Inventive concept 73. The method according to inventive concept        72, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, the length of each one        of the flared ends of the sleeve being less than 40 mm.        Inventive concept 74. The method according to inventive concept        70, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, a length of the narrow        central portion of the sleeve being greater than 3 mm.        Inventive concept 75. The method according to inventive concept        74, wherein placing the sleeve into the blood vessel comprises        placing the sleeve into the blood vessel, the length of the        narrow central portion of the sleeve being less than 70 mm.        Inventive concept 76. A method for operating a blood pump        disposed inside a blood vessel of a subject, the method        comprising:    -   placing an occlusion element in the blood vessel, the occlusion        element having an occluding state thereof, in which the        occlusion element occludes the blood vessel, and a non-occluding        state thereof in which the occlusion element does not occlude        the blood vessel;    -   drawing blood in a downstream direction from a site that is in        fluid communication with an upstream side of the occlusion        element;    -   pumping blood into a site of the subject's vasculature that is        in fluid communication with a downstream side of the occlusion        element,    -   the pumping of the blood into the subject's vasculature being        performed in a manner that maintains the occlusion element in an        occluding state thereof, in which state the occlusion element        occludes the blood vessel.        Inventive concept 77. The method according to inventive concept        76, further comprising performing ultrafiltration on the blood        prior to pumping the blood into the site of the subject's        vasculature.        Inventive concept 78. The method according to inventive concept        76, wherein placing the occlusion element in the blood vessel        comprises placing the occlusion element in the blood vessel for        less than one week, and wherein pumping the blood comprises        pumping the blood into the vasculature for less than one week.        Inventive concept 79. The method according to inventive concept        76, wherein placing the occlusion element in the blood vessel        comprises placing the occlusion element in the blood vessel for        more than one week, and wherein pumping the blood comprises        pumping the blood into the vasculature for less than one week.        Inventive concept 80. The method according to inventive concept        76, further comprising identifying the subject as a subject        suffering from a condition selected from the group consisting        of: cardiac dysfunction, congestive heart failure, reduced renal        blood flow, increased renal vascular resistance, arterial        hypertension, and kidney dysfunction, wherein the blood vessel        includes a renal vein of the subject, and wherein drawing blood        in the downstream direction from the site that is in fluid        communication with the upstream side of the occlusion element        comprises, in response to identifying the subject as suffering        from the condition, reducing blood pressure within the subject's        renal vein by drawing the blood in the downstream direction.        Inventive concept 81. The method according to any one of        inventive concepts 76-80, wherein pumping the blood into the        subject's vasculature in the manner that maintains the occlusion        element in the occluding state thereof comprises pumping the        blood into the subject's vasculature such that hydrodynamic        pressure of the blood that is pumped into the subject's        vasculature maintains the occlusion element in the occluding        state thereof.        Inventive concept 82. The method according to inventive concept        81, wherein placing the occlusion element in the blood vessel        comprises placing within the blood vessel a valve having valve        leaflets, and wherein pumping the blood into the subject's        vasculature such that hydrodynamic pressure of the blood that is        pumped into the subject's vasculature maintains the occlusion        element in the occluding state thereof comprises pumping the        blood into the subject's vasculature such that the blood that is        pumped into the subject's vasculature directly impacts        downstream sides of the valve leaflets.        Inventive concept 83. The method according to inventive concept        82, wherein placing the valve within the blood vessel comprises        placing the valve within the blood vessel such that:    -   in response to blood pressure on an upstream side of the valve        leaflets exceeding pressure on the downstream side of the valve        leaflets, blood flows in an antegrade direction between cusps of        the valve leaflets and an inner wall of the blood vessel, and    -   in response to blood pressure on the downstream side of the        valve leaflets exceeding pressure on the upstream side of the        valve leaflets, the valve occludes retrograde blood flow by the        cusps of the valve leaflets contacting the inner wall of the        blood vessel.        Inventive concept 84. The method according to inventive concept        82, wherein pumping the blood into the subject's vasculature        such that the blood that is pumped into the subject's        vasculature directly impacts downstream sides of the valve        leaflets comprises reducing blood clots at the valve leaflets,        by flushing the valve leaflets.        Inventive concept 85. The method according to inventive concept        82, further comprising pumping an anticoagulation agent into the        subject's vasculature together with the blood that is pumped        into the subject's vasculature, such that the anticoagulation        agent directly impacts the valve leaflets.        Inventive concept 86. The method according to inventive concept        82, wherein placing the valve in the blood vessel comprises        maintaining portions of the valve leaflets in contact with a        wall of the blood vessel by inflating a balloon.        Inventive concept 87. The method according to inventive concept        82, wherein placing the valve in the blood vessel comprises        maintaining portions of the valve leaflets in contact with a        wall of the blood vessel by expanding portions of a slit tube        radially outwardly.        Inventive concept 88. The method according to inventive concept        82, wherein pumping the blood such that the blood directly        impacts the downstream sides of the valve leaflets comprises        pumping the blood into the subject's vasculature via holes that        are shaped to direct the blood toward the downstream sides of        the valve leaflets.        Inventive concept 89. The method according to inventive concept        82, wherein pumping the blood such that the blood directly        impacts the downstream sides of the valve leaflets comprises        pumping the blood into the subject's vasculature via a pump        catheter that is shaped to define a radial protrusion therefrom        that is concavely curved toward a distal end of the catheter,        the radial protrusion being configured to direct blood that is        pumped into the vasculature toward the valve leaflets.        Inventive concept 90. The method according to inventive concept        82, wherein pumping the blood such that the blood directly        impacts the downstream sides of the valve leaflets comprises        pumping the blood into the subject's vasculature via holes that        are disposed adjacent to bases of the valve leaflets.        Inventive concept 91. The method according to inventive concept        90, wherein pumping the blood such that the blood directly        impacts the downstream sides of the valve leaflets comprises        pumping the blood into the subject's vasculature via holes that        are disposed adjacent to a location along lengths of the valve        leaflets that is below midway between cusps of the leaflets and        bases of the leaflets.        Inventive concept 92. Apparatus for use with a blood vessel of a        subject, the apparatus comprising:    -   an occlusion element configured to be placed in the blood        vessel, the occlusion element having an occluding state thereof,        in which the occlusion element occludes the blood vessel, and a        non-occluding state thereof in which the occlusion element does        not occlude the blood vessel;    -   a blood pump configured to:        -   draw blood in a downstream direction from a site that is in            fluid communication with an upstream side of the occlusion            element, and        -   pump blood into the subject's vasculature at a site that is            in fluid communication with a downstream side of the            occlusion element, the pump being configured to perform the            pumping of the blood into the blood vessel in a manner that            maintains the occlusion element in the occluding state            thereof.            Inventive concept 93. The apparatus according to inventive            concept 92, wherein the blood pump is configured to perform            ultrafiltration of the blood prior to pumping the blood into            the subject's vasculature.            Inventive concept 94. The apparatus according to inventive            concept 92, wherein the occlusion element is configured to            be placed in the blood vessel for less than one week, and            the pump is configured to pump blood into the vasculature            for less than one week.            Inventive concept 95. The apparatus according to inventive            concept 92, wherein the occlusion element is configured to            be placed in the blood vessel for more than one week, and            the pump is configured to pump blood into the vasculature            for less than one week.            Inventive concept 96. The apparatus according to any one of            inventive concepts 92-95, wherein the pump is configured to            perform the pumping of the blood into the subject's            vasculature in the manner that maintains the occlusion            element in the occluding state thereof, by pumping the blood            into the subject's vasculature such that hydrodynamic            pressure of the blood that is pumped into the subject's            vasculature maintains the occlusion element in the occluding            state thereof.            Inventive concept 97. The apparatus according to inventive            concept 96, wherein the occlusion element comprises a valve            having valve leaflets, and wherein the pump is configured to            pump the blood into the subject's vasculature such that the            hydrodynamic pressure of the blood maintains the occlusion            element in the occluding state thereof by pumping the blood            into the subject's vasculature such that the blood that is            pumped into the subject's vasculature directly impacts            downstream sides of the valve leaflets.            Inventive concept 98. The apparatus according to inventive            concept 97, wherein the valve is configured such that:    -   in response to blood pressure on an upstream side of the valve        leaflets exceeding pressure on the downstream side of the valve        leaflets, blood flows in an antegrade direction between cusps of        the valve leaflets and an inner wall of the blood vessel, and    -   in response to blood pressure on the downstream side of the        valve leaflets exceeding pressure on the upstream side of the        valve leaflets, the valve closes by the cusps of the valve        leaflets contacting the inner wall of the blood vessel.        Inventive concept 99. The apparatus according to inventive        concept 97, wherein the pump, by pumping the blood into the        subject's vasculature such that the blood that is pumped into        the subject's vasculature directly impacts downstream sides of        the valve leaflets, is configured to reduce blood clots at the        valve leaflets by flushing the valve leaflets.        Inventive concept 100. The apparatus according to inventive        concept 97, wherein the apparatus is for use with an        anticoagulation agent, and wherein the pump is configured to        pump the anticoagulation agent into the subject's vasculature        together with the blood that is pumped into the subject's        vasculature, such that the anticoagulation agent directly        impacts the valve leaflets.        Inventive concept 101. The apparatus according to inventive        concept 97, further comprising a balloon configured to maintain        portions of the valve leaflets in contact with a wall of the        blood vessel by being inflated.        Inventive concept 102. The apparatus according to inventive        concept 97, further comprising a slit tube configured to be        inserted into the blood vessel and to maintain portions of the        valve leaflets in contact with a wall of the blood vessel by        portions of the slit tube between the slits being expanded        radially outwardly.        Inventive concept 103. The apparatus according to inventive        concept 97, wherein the blood pump is configured to be coupled        to the valve, wherein the blood pump comprises outlet holes via        which the blood is pumped into the subject's vasculature, and        wherein the outlet holes are shaped such that when the blood        pump is coupled to the valve, the outlet holes direct the blood        toward the downstream sides of the valve leaflets.        Inventive concept 104. The apparatus according to inventive        concept 97, wherein the blood pump is configured to be coupled        to the valve, wherein the blood pump comprises a blood pump        catheter that defines a radial protrusion therefrom that is        concavely curved toward a distal end of the catheter, the radial        protrusion being configured such that, when the blood pump is        coupled to the valve, the radial protrusion directs blood that        is pumped into the vasculature toward the valve leaflets.        Inventive concept 105. The apparatus according to inventive        concept 97, wherein the blood pump is configured to be coupled        to the valve, wherein the blood pump comprises outlet holes via        which the blood is pumped into the subject's vasculature, and        wherein the outlet holes are disposed on the blood pump such        that, when the blood pump is coupled to the valve, the holes are        disposed adjacent to bases of the valve leaflets.        Inventive concept 106. The apparatus according to inventive        concept 105, wherein the outlet holes are disposed on the blood        pump such that, when the blood pump is coupled to the valve, the        outlet holes are disposed adjacent to a location along lengths        of the valve leaflets that is below midway between cusps of the        leaflets and bases of the leaflets.        Inventive concept 107. Apparatus for use with a blood vessel of        a subject, the apparatus comprising:    -   a blood pump configured to draw blood in a downstream direction        through the blood vessel into the pump; and    -   a valve comprising rigid portions thereof, the rigid portions        being configured to couple the valve to the blood vessel, the        valve being configured to be coupled to a distal portion of the        blood pump and to prevent blood from flowing past the valve in a        retrograde direction.        Inventive concept 108. The apparatus according to inventive        concept 107, wherein the valve further comprises flexible valve        leaflets that are coupled to the rigid portions of the valve.        Inventive concept 109. A method comprising:    -   providing a prosthetic valve that defines valve leaflets; and    -   placing the valve in a blood vessel such that:        -   in response to blood pressure on the upstream side of the            valve leaflets exceeding pressure on the downstream side of            the valve leaflets, blood flows in an antegrade direction            between cusps of the valve leaflets and an inner wall of the            blood vessel, and        -   in response to blood pressure on the downstream side of the            valve leaflets exceeding pressure on the upstream side of            the valve leaflets, the valve closes by the cusps of the            valve leaflets contacting the inner wall of the blood            vessel.            Inventive concept 110. Apparatus comprising:    -   a prosthetic valve that comprises flexible valve leaflets and a        rigid valve frame, the valve leaflets being coupled to the valve        frame such that:    -   in response to pressure on a first side of the valve leaflets        exceeding pressure on a second side of the valve leaflets, the        leaflets open by cusps of the valve leaflets separating from the        rigid frame, and    -   in response to blood pressure on the second side of the valve        leaflets exceeding pressure on the first side of the valve        leaflets, the valve closes by the cusps of the leaflets        contacting the rigid frame.        Inventive concept 111. Apparatus comprising:    -   a blood pump, comprising:        -   a tube;        -   first and second unidirectional valves disposed,            respectively, at proximal and distal ends of the tube;        -   a membrane coupled to the inside of the tube such as to            partition the tube into a first compartment that is in fluid            communication with the valves, and a second compartment that            is not in fluid communication with the valves; and        -   a pumping mechanism configured to pump fluid through the            tube by increasing and subsequently decreasing the size of            the first compartment by moving the membrane with respect to            the tube.            Inventive concept 112. The apparatus according to inventive            concept 111, wherein the tube comprises a stent, and            material disposed on the stent.            Inventive concept 113. The apparatus according to inventive            concept 111, wherein the occlusion element is configured to            be placed in a blood vessel for less than one week.            Inventive concept 114. The apparatus according to inventive            concept 111, wherein one of the valves is configured to            prevent backflow of blood from the tube into the blood            vessel and a second one of the valves is configured to            prevent backflow of blood from the blood vessel into the            tube.            Inventive concept 115. The apparatus according to any one of            inventive concepts 111-114, wherein the blood pump is            configured to be placed in a renal vein of a subject and to            pump blood in a downstream direction from the renal vein to            a vena cava of the subject.            Inventive concept 116. The apparatus according to inventive            concept 115, wherein the blood pump is configured to occlude            backflow of blood from the vena cava to the renal vein.            Inventive concept 117. A method, comprising:    -   coupling a tube to an inner wall of a blood vessel of a subject,        -   first and second unidirectional valves being disposed,            respectively, at proximal and distal ends of the tube, and        -   a membrane being coupled to the inside of the tube, such as            to partition the tube into a first compartment that is in            fluid communication with the valves, and a second            compartment that is not in fluid communication with the            valves; and    -   operating a pumping mechanism to pump blood through the tube by        increasing and subsequently decreasing the size of the first        compartment, by moving the membrane with respect to the tube.        Inventive concept 118. The method according to inventive concept        117, wherein the tube includes a stent and material disposed on        the stent, and wherein coupling the tube to the inner wall of        the blood vessel comprises coupling the stent and the material        to the inner wall of the blood vessel.        Inventive concept 119. The method according to inventive concept        117, wherein coupling the tube to the inner wall of the blood        vessel comprises coupling the tube to the inner wall of the        blood vessel for less than one week.        Inventive concept 120. The method according to inventive concept        117, wherein operating the pumping mechanism comprises operating        the pumping mechanism such that one of the valves prevents        backflow of blood from the tube into the blood vessel and a        second one of the valves prevents backflow of blood from the        blood vessel into the tube.        Inventive concept 121. The method according to any one of        inventive concepts 117-120, wherein coupling the tube to the        inner wall of the blood vessel comprises coupling the tube to an        inner wall of a renal vein of a subject, and wherein operating        the pumping mechanism comprises pumping blood in a downstream        direction from the renal vein to a vena cava of the subject.        Inventive concept 122. The method according to inventive concept        121, wherein coupling the tube to the inner wall of the renal        vein comprises occluding backflow of blood from the vena cava to        the renal vein.        Inventive concept 123. The method according to inventive concept        121, further comprising identifying the subject as a subject        suffering from a condition selected from the group consisting        of: cardiac dysfunction, congestive heart failure, reduced renal        blood flow, increased renal vascular resistance, arterial        hypertension, and kidney dysfunction, wherein operating the pump        comprises, in response to identifying the subject as suffering        from the condition, reducing blood pressure within the subject's        renal vein by operating the pump to pump blood in the downstream        direction from the renal vein to the vena cava.        Inventive concept 124. A method comprising:    -   operating a blood pump to pump blood in a downstream direction        through a first vein, the first vein being a tributary of a        second vein and forming a junction with the second vein; and    -   preventing backflow of blood from the second vein to the first        vein by covering an ostium at the junction with an        ostium-covering umbrella disposed in the second vein.        Inventive concept 125. The method according to inventive concept        124, wherein operating the blood pump comprises performing        ultrafiltration on the pumped blood.        Inventive concept 126. The method according to inventive concept        124, wherein the ostium-covering umbrella includes an        ostium-covering umbrella having a diameter of more than 6 mm        when in an open configuration, and wherein covering the ostium        with the umbrella comprises covering the ostium with the        umbrella having a diameter of more than 6 mm.        Inventive concept 127. The method according to inventive concept        124, wherein operating the blood pump comprises causing the        ostium-covering umbrella to become sealed against a wall of the        second vein surrounding the ostium.        Inventive concept 128. The method according to any one of        inventive concepts 124-127, wherein the first vein includes a        renal vein of the subject, and the second vein includes a vena        cava of the subject, and wherein pumping blood in the downstream        direction comprises pumping blood in a downstream direction from        the renal vein toward the vena cava.        Inventive concept 129. The method according to inventive concept        128, wherein preventing backflow of blood from the second vein        to the first vein comprises preventing backflow of blood from        the vena cava to the renal vein.        Inventive concept 130. The method according to inventive concept        128, further comprising identifying the subject as a subject        suffering from a condition selected from the group consisting        of: cardiac dysfunction, congestive heart failure, reduced renal        blood flow, increased renal vascular resistance, arterial        hypertension, and kidney dysfunction, wherein operating the pump        comprises, in response to identifying the subject as suffering        from the condition, reducing blood pressure within the subject's        renal vein by operating the pump to pump blood in the downstream        direction from the renal vein to the vena cava.        Inventive concept 131. Apparatus for use with a first vein of a        subject, the first vein being a tributary of a second vein and        forming a junction with the second vein, the apparatus        comprising:    -   a catheter configured to be placed in the first vein, a distal        end of the catheter being configured to pump blood in a        downstream direction through the first vein and into the        catheter; and    -   an ostium-covering umbrella disposed around the outside of the        catheter and configured to be placed within the second vein at        the junction such that the umbrella prevents backflow of blood        from the second vein to the first vein by the ostium-occluding        umbrella covering an ostium at the junction from a location        within the second vein.        Inventive concept 132. The apparatus according to inventive        concept 131, wherein the catheter, by pumping the blood is        configured to cause the ostium-covering umbrella to become        sealed against a wall of the second vein surrounding the ostium.        Inventive concept 133. The apparatus according to inventive        concept 131, wherein the ostium-covering umbrella has a diameter        of more than 6 mm, when in an open configuration.        Inventive concept 134. The apparatus according to any one of        inventive concepts 131-133, wherein the first vein includes a        renal vein of the subject, and the second vein includes a vena        cava of the subject, and wherein the catheter is configured to        pump blood by pumping blood in a downstream direction from the        renal vein.        Inventive concept 135. The apparatus according to inventive        concept 134, wherein the ostium-covering umbrella is configured        to prevent backflow of blood from the vena cava to the renal        vein by the ostium-occluding umbrella covering an ostium at a        junction of the renal vein and the vena cava, from a location        within the vena cava.        Inventive concept 136. Apparatus comprising:    -   a catheter;    -   a pumping mechanism configured to suction fluid into a distal        end of the catheter; and    -   an ostium-covering umbrella disposed around the outside of the        catheter, the umbrella having a diameter of at least 6 mm when        in an open configuration thereof.        Inventive concept 137. The apparatus according to inventive        concept 136, wherein the diameter of the ostium-covering        umbrella is between 10 mm and 20 mm.        Inventive concept 138. The apparatus according to inventive        concept 136, wherein the diameter of the ostium-covering        umbrella is between 15 mm and 25 mm.        Inventive concept 139. A method for measuring flow in a blood        vessel comprising:    -   occluding the blood vessel with an occlusion element;    -   pumping blood from an upstream side of the occlusion element to        a downstream side of the occlusion element;    -   measuring blood pressure on the upstream and downstream sides of        the occlusion element;    -   modulating the pumping such that pressure on the downstream side        of the occlusion element is equal to pressure on the upstream        side of the occlusion element;    -   measuring a flow rate of blood through the pump when the        pressure on the downstream side of the occlusion element is        equal to pressure on the upstream side of the occlusion element;    -   designating the measured flow rate as a baseline flow rate; and    -   subsequently, measuring a flow rate of blood through the pump        relative to the baseline flow rate.        Inventive concept 140. The method according to inventive concept        139, further comprising, in response to designating the baseline        flow rate, designating a baseline measure of vascular resistance        of the subject, and subsequently, measuring vascular resistance        of the subject relative to the baseline vascular resistance.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

The invention claimed is:
 1. A method for improving renal function of apatient, comprising: using an occluding element that is placed in aninferior vena cava of the patient at a location that is downstream of arenal vein ostium, at least partially mechanically occluding theinferior vena cava of the patient downstream of the renal vein ostium,such as to form a compartment within the inferior vena cava that isisolated from a downstream region of the inferior vena cava that isdownstream of the renal vein ostium; and using a blood pump that isseparate from the occluding element, and that is placed in thecompartment, mechanically pumping blood through the inferior vena cavafrom the compartment to a discharge location in the downstream regionwhile the inferior vena cava is at least partially occluded, wherein theblood remains in the inferior vena cava throughout the mechanicalpumping of the blood from the compartment to the discharge location. 2.The method of claim 1, wherein mechanically pumping blood comprisesplacing a catheter-based pump within the compartment.
 3. The method ofclaim 2, wherein placing the catheter-based pump within the compartmentcomprises placing an impeller pump within the compartment.
 4. A methodfor improving renal function of a patient, comprising: using anoccluding element that is placed in an inferior vena cava of the patientat a location that is downstream of a renal vein ostium, at leastpartially mechanically occluding the inferior vena cava of the patientdownstream of the renal vein ostium, such as to form a compartmentwithin the inferior vena cava that is isolated from a downstream regionof the inferior vena cava that is downstream of the renal vein ostium;and using a blood pump that is separate from the occluding element, andthat is placed in the compartment, mechanically pumping blood throughthe inferior vena cava from the compartment to a discharge location inthe downstream region while the inferior vena cava is at least partiallyoccluded, wherein the blood does not leave the inferior vena cava whilebeing mechanically pumped.
 5. The method of claim 4, whereinmechanically pumping blood comprises placing a catheter-based pumpwithin the compartment.
 6. The method of claim 5, wherein placing thecatheter-based pump within the compartment comprises placing an impellerpump within the compartment.
 7. A method for improving renal function ofa patient, comprising: using an occluding element that is placed in aninferior vena cava of the patient at a location that is downstream of arenal vein ostium, at least partially mechanically occluding theinferior vena cava of a vasculature of the patient downstream of therenal vein ostium, such as to form a compartment within the inferiorvena cava that is isolated from a downstream region of the inferior venacava that is downstream of the renal vein ostium; and using a blood pumpthat is separate from the occluding element, and that is placed in thecompartment, mechanically pumping blood through the inferior vena cavafrom the compartment to a discharge location in the downstream regionwhile the inferior vena cava is at least partially occluded, wherein theblood does not leave the vasculature of the patient while beingmechanically pumped.
 8. The method of claim 7, wherein mechanicallypumping blood comprises placing a catheter-based pump within thecompartment.
 9. The method of claim 8, wherein placing thecatheter-based pump within the compartment comprises placing an impellerpump within the compartment.